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Labels: Garden, Gardening, Greenhouse, Lawn, Lawn Care, Plants., Rose, Rose Gardening
posted by seli at
7:44 PM
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Monday, January 12, 2009
Monday, November 19, 2007
posted by seli at
11:05 PM
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Steering Tomatoes
This article should, preferably, be read after reading the article on General irrigation principles for greenhouse crops grown in media
In the wild, tomatoes tend to grow vegetatively (growing stems and leaves) when they are young plants in spring but when they have grown to a reasonable size going into summer, change to generative growing (most effort put into flowers, buds and fruit).
Modern tomato growers, however, want to grow the plants for 10 or more months, right into winter when prices are high. To do this they need to steer the plants away from its natural tendency to grow too generatively in summer and also to avoid it becoming too vegetative in cool, low light conditions as winter is approached. Growers call this balancing the plant and spend considerable time and energy achieving this as it has a major effect on quality, disease control and yield. In addition, optimizing the watering regimen minimizes wastage of water and fertilizer and reduces harm to the environment.
Warm, high light, low humidity, summer conditions steer the plant toward generative growth and cooler, lower light conditions toward more vegetative growth. This means that it is difficult to keep the plants growing with some vegetative tendency in summer and to stop them becoming too vegetative in cooler, dull conditions. At these times, manipulating the root zone conditions in conjunction with environmental conditions can be particularly advantageous.
Conditions that encourage vegetative growth include:-
Environmental
Less intense light
Cooler temperatures
Large day-night temperature difference
Root-zone
Wetter root conditions
Many small irrigations
Starting watering earlier and stopping later in the day
Lower EC in root zone
Less dry down over night (4% to 6%)
High nitrogen fertilizer mix
Conditions that favour generative growth include:-
Environmental
More intense light
Warmer temperatures
Small day-night temperature difference (but if too small, flower set may fail)
Root-zone
Dryer root conditions
Fewer large irrigations
Higher EC in root zone
More dry down over night (8% to 12%)
Starting watering later and stopping earlier in the day
Things are not as simple as that though, as excesses of some of these influences can create other problems and sensible limits must be applied. In fact, many of the changes that can steer toward vegetative can also cause fruit split or cause disease problems if overdone especially if implemented after conditions have allowed to become too generative for any period of time.
Much steering can be done by adjusting the irrigation EC (increase in low light conditions and lower in bright conditions), by adjusting the watering start and stop times and by changing the irrigation duration and frequency.
For night dry down, it is normally considered that a dry down of 4 to 6% will be generative and 8 to 12% will be generative. Lower than 4% and you might be looking at poor root development and subsequent disease problems. Too dry and it will be difficult to wet up again the next day. In general, changes to the media moisture content should be made slowly at say 1% change per day.
The watering start time must be close to sunrise. Too much before sunrise and there is a risk of splitting the fruit. Too far after sun rise, may make it difficult to wet up for the day as the crop will already be taking water from the media before watering commences.
The watering stop time is frequently manipulated to steer the plant. Stopping earlier will cause greater dry down and steer toward generative. The average time to stop is when it is estimated that there will be a further 200 to 300 Joules/cm2 of light energy received before dusk. Obviously, this has to be an estimation based on expected weather and previous days experience, watching carefully to see what dry down was actually achieved the night(s) before. The exact setting will also depend on the growers observations ie is the crop.
To determine if the crop is tending toward veg or gen, observations and measurements are made on the crop as described below. Bear in mind that exact dimensions and observations will depend on the specific cultivar.
Crop observations:-
Measure length between highest flower truss and growing tip (long = veg; short = gen)
Measure diameter of growing head (large and open = veg; small and tight = gen)
Colour of leaves and flowers (light = veg; dark = gen)
Diameter of stem (thin = veg; thick = gen)
Truss curled indicates generative growth
For some common tomato varieties, the flower truss to tip is typically about 14cm and the stem diameter is 11mm for a “balanced” plant.
These observations are then used to alter the growing conditions to steer the crop back to a more balanced position.
Example
Lets assume that we have had a period of very hot, dry weather and observations indicate that the crop is becoming overly generative. Here are some of the things that can be done.
To steer back to a more vegetative position:-
Try to provide extra cooling and humidification in the greenhouse. This can be achieved by fogging during the day and/or providing increased shading.
On the irrigation side look carefully at the run-off EC. It is likely that this is on the high side. Normally the run-off EC will start the day high and drop back to the desired EC soon after mid-day. If it is staying high and has a big differential as compared with the irrigation EC then you need to increase watering during the day. This can be done by either lowering the solar integration trigger (so it waters more often) or by increasing the irrigation duration so that more water is applied when it irrigates. From what we have said earlier, it is the solar integration trigger that will have the biggest effect on steering toward veg. Also, check that run-off is adequate eg 30% during the afternoon and that it starts early enough in the day (by about 10:30am for example)
If, on the other hand the EC is high but not excessively different from the irrigation water, then lowering the irrigation EC a bit will help. A typical summer setting may be irrigation EC of 2.0 expecting a run-off EC of 3.0 to 3.5.
The other correction to make is to check the irrigation start time is not too late and also adjust the stop time to ensure there is not excessive dry down overnight. Normally, stop time is set to about 2hours (or 250J/cm2) before sunset hoping to achieve a dry down of between 2% to 4% by sunset.
In very exceptionally dry cases it may be necessary to have a scheduled small irrigation during the night but normally just adjusting the stop time will solve this problem.
Whilst this article may provide the grower with a better understanding of some of the general principles of crop steering by root-zone control, it is important to get advice from a horticultural consultant that is familiar with the particular climate and crop variety.
Jeff Broad
Autogrow Systems Ltd
This article should, preferably, be read after reading the article on General irrigation principles for greenhouse crops grown in media
In the wild, tomatoes tend to grow vegetatively (growing stems and leaves) when they are young plants in spring but when they have grown to a reasonable size going into summer, change to generative growing (most effort put into flowers, buds and fruit).
Modern tomato growers, however, want to grow the plants for 10 or more months, right into winter when prices are high. To do this they need to steer the plants away from its natural tendency to grow too generatively in summer and also to avoid it becoming too vegetative in cool, low light conditions as winter is approached. Growers call this balancing the plant and spend considerable time and energy achieving this as it has a major effect on quality, disease control and yield. In addition, optimizing the watering regimen minimizes wastage of water and fertilizer and reduces harm to the environment.
Warm, high light, low humidity, summer conditions steer the plant toward generative growth and cooler, lower light conditions toward more vegetative growth. This means that it is difficult to keep the plants growing with some vegetative tendency in summer and to stop them becoming too vegetative in cooler, dull conditions. At these times, manipulating the root zone conditions in conjunction with environmental conditions can be particularly advantageous.
Conditions that encourage vegetative growth include:-
Environmental
Less intense light
Cooler temperatures
Large day-night temperature difference
Root-zone
Wetter root conditions
Many small irrigations
Starting watering earlier and stopping later in the day
Lower EC in root zone
Less dry down over night (4% to 6%)
High nitrogen fertilizer mix
Conditions that favour generative growth include:-
Environmental
More intense light
Warmer temperatures
Small day-night temperature difference (but if too small, flower set may fail)
Root-zone
Dryer root conditions
Fewer large irrigations
Higher EC in root zone
More dry down over night (8% to 12%)
Starting watering later and stopping earlier in the day
Things are not as simple as that though, as excesses of some of these influences can create other problems and sensible limits must be applied. In fact, many of the changes that can steer toward vegetative can also cause fruit split or cause disease problems if overdone especially if implemented after conditions have allowed to become too generative for any period of time.
Much steering can be done by adjusting the irrigation EC (increase in low light conditions and lower in bright conditions), by adjusting the watering start and stop times and by changing the irrigation duration and frequency.
For night dry down, it is normally considered that a dry down of 4 to 6% will be generative and 8 to 12% will be generative. Lower than 4% and you might be looking at poor root development and subsequent disease problems. Too dry and it will be difficult to wet up again the next day. In general, changes to the media moisture content should be made slowly at say 1% change per day.
The watering start time must be close to sunrise. Too much before sunrise and there is a risk of splitting the fruit. Too far after sun rise, may make it difficult to wet up for the day as the crop will already be taking water from the media before watering commences.
The watering stop time is frequently manipulated to steer the plant. Stopping earlier will cause greater dry down and steer toward generative. The average time to stop is when it is estimated that there will be a further 200 to 300 Joules/cm2 of light energy received before dusk. Obviously, this has to be an estimation based on expected weather and previous days experience, watching carefully to see what dry down was actually achieved the night(s) before. The exact setting will also depend on the growers observations ie is the crop.
To determine if the crop is tending toward veg or gen, observations and measurements are made on the crop as described below. Bear in mind that exact dimensions and observations will depend on the specific cultivar.
Crop observations:-
Measure length between highest flower truss and growing tip (long = veg; short = gen)
Measure diameter of growing head (large and open = veg; small and tight = gen)
Colour of leaves and flowers (light = veg; dark = gen)
Diameter of stem (thin = veg; thick = gen)
Truss curled indicates generative growth
For some common tomato varieties, the flower truss to tip is typically about 14cm and the stem diameter is 11mm for a “balanced” plant.
These observations are then used to alter the growing conditions to steer the crop back to a more balanced position.
Example
Lets assume that we have had a period of very hot, dry weather and observations indicate that the crop is becoming overly generative. Here are some of the things that can be done.
To steer back to a more vegetative position:-
Try to provide extra cooling and humidification in the greenhouse. This can be achieved by fogging during the day and/or providing increased shading.
On the irrigation side look carefully at the run-off EC. It is likely that this is on the high side. Normally the run-off EC will start the day high and drop back to the desired EC soon after mid-day. If it is staying high and has a big differential as compared with the irrigation EC then you need to increase watering during the day. This can be done by either lowering the solar integration trigger (so it waters more often) or by increasing the irrigation duration so that more water is applied when it irrigates. From what we have said earlier, it is the solar integration trigger that will have the biggest effect on steering toward veg. Also, check that run-off is adequate eg 30% during the afternoon and that it starts early enough in the day (by about 10:30am for example)
If, on the other hand the EC is high but not excessively different from the irrigation water, then lowering the irrigation EC a bit will help. A typical summer setting may be irrigation EC of 2.0 expecting a run-off EC of 3.0 to 3.5.
The other correction to make is to check the irrigation start time is not too late and also adjust the stop time to ensure there is not excessive dry down overnight. Normally, stop time is set to about 2hours (or 250J/cm2) before sunset hoping to achieve a dry down of between 2% to 4% by sunset.
In very exceptionally dry cases it may be necessary to have a scheduled small irrigation during the night but normally just adjusting the stop time will solve this problem.
Whilst this article may provide the grower with a better understanding of some of the general principles of crop steering by root-zone control, it is important to get advice from a horticultural consultant that is familiar with the particular climate and crop variety.
Jeff Broad
Autogrow Systems Ltd
Labels: Autogrow Systems, Steering Tomatoes
posted by seli at
10:52 PM
|
0 Comments
Fertigation Controllers
Fertigation is the irrigation of plants with nutrient enriched (and possibly pH corrected) water. A full fertigation controller is thus a combination of a multi-station horticultural irrigation controller and a fertiliser injection system.
A modern fertigation controller like the NutriDose II range will normally have a variety of trigger sources to start irrigations including time-of-day programmed irrigations, solar integration triggering possibly with the ability to modify the integration rate to compensate for humidity, temperature and wind speed. The solar integrator (with temperature and humidity modifiers) will automatically increase the frequency of irrigations in sunny, hot dry weather and reduce it in dull, cool, damp weather. A rain override is useful for outdoor crops as it can be set to zero the integration counter if rain exceeds a specified level.
These controllers may generate a single irrigation trigger and then sequentially irrigate all stations in turn. The Autogrow controllers can be set to do this or can be put into multi-trigger mode where each station has its own trigger point and when reached only that station will be irrigated. This allows crops with differing watering requirements to be serviced by a common controller. In fact with the NutriDose IIb or NutriDose IIi it would be possible to mix inside with outside crops and crops requiring watering every half hour with those that need watering once per week. Of-course each station can be set to have a different EC and may even be fed with a mixture having a different recipe.
It is important that the solar integrator, fertiliser injection and irrigation functions are all within the same controller as this provides the highest level of functionality. For example, if a separate solar integrator was used, the manual triggering of an irrigation will not be “seen” by the solar integrator and so its counter will continue counting. The solar integrator will not have its counter cleared and may trigger a second irrigation immediately after the manual one. In the case of an integrated controller this will automatically be taken care of.
Using an electronic controller employing feedback control allows a number of different methods to be used to actually get the fertiliser into the pipe. The first and most obvious method uses variable speed injection pumps to inject direct into the line. This becomes very expensive as soon as larger flow rates are required. The second method uses venturi eductors to entrain the nutrient and pH stock solutions into the flow of water through them. To adjust the rate of nutrient uptake it is common to use simple on/off solenoid valves that continuously pulse on and off. By varying the ratio of the on time to the off time good proportional control can be achieved. This method is usually called “pulse width modulated” (PWM) control. To work reliably the venturis need a significant pressure drop across them and this normally leads to an auxiliary pump being required to develop this. This is a simple robust method but does require high pressure sensors in the line and also the system design must ensure satisfactory mixing occurs before the concentrated stock solutions are allowed to mix with each other. If they meet in concentrated form a chemical reaction can take place which will change the formulation of the fertiliser. In addition, the resulting precipitation can cause solids that can later block drippers and be a general nuisance.
The last method uses an in-line turbulent mixing vessel into which the fertiliser stock solutions are dosed. This method provides excellent mixing and has the advantage that the dosing and sensing is done at ambient pressure. Typically a drum of one-to-two hundred litres capacity is used and is filled at the same rate as it is being emptied.
The NutriDose IIi controller can be used in all three of the above methods, has a built-in solar integrator counters, irrigation control and interface to a PC to provide a user friendly interface, remote alarms and data and event logging. It can be expanded up to a maximum of thirty irrigation stations which may be a mixture of inside and outdoor growing areas.
The NutriDose IIb controller performs a similar function but is a batching controller. Instead of adding the fertiliser on-the-fly during an irrigation, a batching controller mixes a complete batch of fertilised water into a batching tank which is then used for irrigation. This is a simpler process and tends to be a little lower in cost and is also easier to set up to get really high accuracy. In other respects it is the same as the NutriDose IIi and can be used in multiple batch – multiple trigger, single batch – single trigger, single batch – multiple trigger and multiple batch – single trigger modes. The down side of batched irrigation is that time is used in mixing the batches and in a large installation or one where very frequent irrigations are required, it is possible to run out of time and triggers may start to queue up and causing excessive delays in the irrigation of some stations.
Fertigation is the irrigation of plants with nutrient enriched (and possibly pH corrected) water. A full fertigation controller is thus a combination of a multi-station horticultural irrigation controller and a fertiliser injection system.
A modern fertigation controller like the NutriDose II range will normally have a variety of trigger sources to start irrigations including time-of-day programmed irrigations, solar integration triggering possibly with the ability to modify the integration rate to compensate for humidity, temperature and wind speed. The solar integrator (with temperature and humidity modifiers) will automatically increase the frequency of irrigations in sunny, hot dry weather and reduce it in dull, cool, damp weather. A rain override is useful for outdoor crops as it can be set to zero the integration counter if rain exceeds a specified level.
These controllers may generate a single irrigation trigger and then sequentially irrigate all stations in turn. The Autogrow controllers can be set to do this or can be put into multi-trigger mode where each station has its own trigger point and when reached only that station will be irrigated. This allows crops with differing watering requirements to be serviced by a common controller. In fact with the NutriDose IIb or NutriDose IIi it would be possible to mix inside with outside crops and crops requiring watering every half hour with those that need watering once per week. Of-course each station can be set to have a different EC and may even be fed with a mixture having a different recipe.
It is important that the solar integrator, fertiliser injection and irrigation functions are all within the same controller as this provides the highest level of functionality. For example, if a separate solar integrator was used, the manual triggering of an irrigation will not be “seen” by the solar integrator and so its counter will continue counting. The solar integrator will not have its counter cleared and may trigger a second irrigation immediately after the manual one. In the case of an integrated controller this will automatically be taken care of.
Using an electronic controller employing feedback control allows a number of different methods to be used to actually get the fertiliser into the pipe. The first and most obvious method uses variable speed injection pumps to inject direct into the line. This becomes very expensive as soon as larger flow rates are required. The second method uses venturi eductors to entrain the nutrient and pH stock solutions into the flow of water through them. To adjust the rate of nutrient uptake it is common to use simple on/off solenoid valves that continuously pulse on and off. By varying the ratio of the on time to the off time good proportional control can be achieved. This method is usually called “pulse width modulated” (PWM) control. To work reliably the venturis need a significant pressure drop across them and this normally leads to an auxiliary pump being required to develop this. This is a simple robust method but does require high pressure sensors in the line and also the system design must ensure satisfactory mixing occurs before the concentrated stock solutions are allowed to mix with each other. If they meet in concentrated form a chemical reaction can take place which will change the formulation of the fertiliser. In addition, the resulting precipitation can cause solids that can later block drippers and be a general nuisance.
The last method uses an in-line turbulent mixing vessel into which the fertiliser stock solutions are dosed. This method provides excellent mixing and has the advantage that the dosing and sensing is done at ambient pressure. Typically a drum of one-to-two hundred litres capacity is used and is filled at the same rate as it is being emptied.
The NutriDose IIi controller can be used in all three of the above methods, has a built-in solar integrator counters, irrigation control and interface to a PC to provide a user friendly interface, remote alarms and data and event logging. It can be expanded up to a maximum of thirty irrigation stations which may be a mixture of inside and outdoor growing areas.
The NutriDose IIb controller performs a similar function but is a batching controller. Instead of adding the fertiliser on-the-fly during an irrigation, a batching controller mixes a complete batch of fertilised water into a batching tank which is then used for irrigation. This is a simpler process and tends to be a little lower in cost and is also easier to set up to get really high accuracy. In other respects it is the same as the NutriDose IIi and can be used in multiple batch – multiple trigger, single batch – single trigger, single batch – multiple trigger and multiple batch – single trigger modes. The down side of batched irrigation is that time is used in mixing the batches and in a large installation or one where very frequent irrigations are required, it is possible to run out of time and triggers may start to queue up and causing excessive delays in the irrigation of some stations.
Labels: Autogrow Systems, Fertigation Controllers
posted by seli at
10:49 PM
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0 Comments
Nutrient measurement and control
EC, CF and TDS(ppm) - just what are they?
First of all lets dispel the myth that they are all the same sort of measure - they are not. TDS(ppm) refers to the actual quantity of a salt or salts in solution (Total Dissolved Solids) whereas EC and CF refer to the electrical conductivity (ie how easily the solution passes an electric current). Now, we can measure EC (CF) quite easily by passing a high frequency AC current through the solution but we cannot directly measure ppm. EC is measured in mS/cm (milli Siemens per centi metre) and CF is measured in units 1/10 of a mS/cm so the conversion between CF and EC is 1 EC (mS/cm) = 10CF.
So what about measuring the EC and then multiplying the answer by a conversion constant to tell us what the ppm is. Unfortunately, this cannot be done for the simple reason that the conversion constant for every salt is different. Beware of meters that provide a read-out in ppm, they will only give a correct reading for one particular salt - usually sodium chloride. This is unfortunate as sodium chloride has a very different conversion constant from most hydroponic salts and will therefore give a reading that has a very large error. In fact TDS meters usually are calibrated to comply with one of three standards namely NaCl (1mS = 500ppm), 442 (1mS = 700ppm)and some have an imperical standard of 1mS = 650ppm). If you are following instructions from a book or nutrient supplier that is in ppm you need to ensure that you meter is using the same conversion coefficient as the instructions.
Back to the measuring process. High frequency AC is used to try to eliminate electrolysis and the accompanying electroplating of the electrodes. Even so some plating will occur and for this reason it is important to regularly (every two weeks or so) clean the face of the sensor with an abrasive that will remove any such hard plating. Autogrow recommends using a kitchen cleaner such as Jif on a soft cloth or finger tip. Note that plain Jif should be used - not the lemon scented variety as this contains oils that will give an incorrect reading. After cleaning, rinse the electrode in fresh water and shake off the excess. If the probe has a shroud, replace this fully, ensuring that it is impossible to trap air bubbles at the tip when it is stood vertically in water. Do not touch the sensor face with your fingers as these may have oil from perspiration on them. After cleaning, the calibration of the instrument should be checked and recalibrated if necessary. When doing this allow plenty of time for the temperature of the probe to equalise to that of the test solution. All modern EC measurement probes will have a built-in temperature sensor to compensate for the inherent temperature sensitivity of liquid conductivity and this must be given sufficient time to kick-in. Most hydroponic supply stores carry EC (CF) standard solution. This is usually standardised to an EC of 2.77 mS (27.7CF) at 25 Deg C. Note that most modern instruments have built-in temperature compensation and so calibration can be done at any temperature. For good accuracy, it is important to allow the probe to stand in the cal solution for at least 5 minutes so that the temperature of the probe equalises to the temperature of the cal solution.
pH measurement
pH electrodes work like very weak batteries. When placed in a solution they produce a tiny voltage that is proportional to the pH of the liquid. Unfortunately, they have a very high internal impedance and so the voltage cannot be measured by a normal multimeter. pH meters use special amplifiers which present very little load to the sensor in order to measure the voltage accurately.
pH sensors last between 1 and 2 years (3 years if you are really lucky) in a hydroponic system. You should probably change it after 2 years in any event before it really lets you down at the wrong time. To help them last as long as possible you should store them in plain clean water (not distilled) preferably with a little pH4 buffer added. Never let them dry out.
pH instruments are very susceptible to moisture and extreme temperatures so always keep them in a cool dry place and take care not to wet them (even the waterproof ones).
pH electrodes drift quite quickly and their calibration should be checked (and corrected if necessary) every week or two. For hydroponics, this is usually done at pH7 and then at pH4. This provides two calibration points on either side of the usual working value of pH5.5 to pH6.0. Note that modern research has shown the optimum pH value in hydroponics to be lower than the optimum for soil (usually pH6.0 to pH6.5)
On-demand dosers
These are used to automatically maintain the EC and pH at their respective set-points.
Most sensible recirculating hydroponic systems use a reservoir tank that has an automatic water make-up valve (ball cock). As the plants transpire, the water level in the tank falls and fresh water enters the system. This will tend to dilute the nutrient and may also have an effect on the pH. With an on-demand doser, the situation is continually corrected and the ideal EC and pH maintained at all times. This avoids the sudden shock associated with infrequent hand dosing.
Autogrow introduced the worlds first "timed dose" doser about 15 years ago (well, as far as we can tell). This gives a fixed size dose (user settable) when it detects that the EC is low and then waits for a few minutes (user settable) for the dose to mix-in before checking to see if another dose is needed. This method is extremely easy to set up and is not prone to overdosing like many other methods. For this reason other manufacturers are starting to copy the idea.
Many growers like to use a lower EC value during the heat of the day and raise it late afternoon through to the following morning. The new Autogrow NutriDose 1, as well as our greenhouse controllers, have two EC settings corresponding to two time zones to allow this to happen automatically. The NutriDose 1 can even add extra water to reduce the EC
During bright weather, plants grow strong with short internode spacing whereas in dull weather they tend to stretch and grow spindly. To compensate for this, growers will increase the EC during dull weather and lower it in bright weather. Some Autogrow greenhouse controllers will even do this function automatically, within limits specified by the grower.
So, this raises the question; can you exercise the same level of control as can be achieved with modern automatic doser?
Check out the NutriDose series or the mini-dosers for the home gardener
EC, CF and TDS(ppm) - just what are they?
First of all lets dispel the myth that they are all the same sort of measure - they are not. TDS(ppm) refers to the actual quantity of a salt or salts in solution (Total Dissolved Solids) whereas EC and CF refer to the electrical conductivity (ie how easily the solution passes an electric current). Now, we can measure EC (CF) quite easily by passing a high frequency AC current through the solution but we cannot directly measure ppm. EC is measured in mS/cm (milli Siemens per centi metre) and CF is measured in units 1/10 of a mS/cm so the conversion between CF and EC is 1 EC (mS/cm) = 10CF.
So what about measuring the EC and then multiplying the answer by a conversion constant to tell us what the ppm is. Unfortunately, this cannot be done for the simple reason that the conversion constant for every salt is different. Beware of meters that provide a read-out in ppm, they will only give a correct reading for one particular salt - usually sodium chloride. This is unfortunate as sodium chloride has a very different conversion constant from most hydroponic salts and will therefore give a reading that has a very large error. In fact TDS meters usually are calibrated to comply with one of three standards namely NaCl (1mS = 500ppm), 442 (1mS = 700ppm)and some have an imperical standard of 1mS = 650ppm). If you are following instructions from a book or nutrient supplier that is in ppm you need to ensure that you meter is using the same conversion coefficient as the instructions.
Back to the measuring process. High frequency AC is used to try to eliminate electrolysis and the accompanying electroplating of the electrodes. Even so some plating will occur and for this reason it is important to regularly (every two weeks or so) clean the face of the sensor with an abrasive that will remove any such hard plating. Autogrow recommends using a kitchen cleaner such as Jif on a soft cloth or finger tip. Note that plain Jif should be used - not the lemon scented variety as this contains oils that will give an incorrect reading. After cleaning, rinse the electrode in fresh water and shake off the excess. If the probe has a shroud, replace this fully, ensuring that it is impossible to trap air bubbles at the tip when it is stood vertically in water. Do not touch the sensor face with your fingers as these may have oil from perspiration on them. After cleaning, the calibration of the instrument should be checked and recalibrated if necessary. When doing this allow plenty of time for the temperature of the probe to equalise to that of the test solution. All modern EC measurement probes will have a built-in temperature sensor to compensate for the inherent temperature sensitivity of liquid conductivity and this must be given sufficient time to kick-in. Most hydroponic supply stores carry EC (CF) standard solution. This is usually standardised to an EC of 2.77 mS (27.7CF) at 25 Deg C. Note that most modern instruments have built-in temperature compensation and so calibration can be done at any temperature. For good accuracy, it is important to allow the probe to stand in the cal solution for at least 5 minutes so that the temperature of the probe equalises to the temperature of the cal solution.
pH measurement
pH electrodes work like very weak batteries. When placed in a solution they produce a tiny voltage that is proportional to the pH of the liquid. Unfortunately, they have a very high internal impedance and so the voltage cannot be measured by a normal multimeter. pH meters use special amplifiers which present very little load to the sensor in order to measure the voltage accurately.
pH sensors last between 1 and 2 years (3 years if you are really lucky) in a hydroponic system. You should probably change it after 2 years in any event before it really lets you down at the wrong time. To help them last as long as possible you should store them in plain clean water (not distilled) preferably with a little pH4 buffer added. Never let them dry out.
pH instruments are very susceptible to moisture and extreme temperatures so always keep them in a cool dry place and take care not to wet them (even the waterproof ones).
pH electrodes drift quite quickly and their calibration should be checked (and corrected if necessary) every week or two. For hydroponics, this is usually done at pH7 and then at pH4. This provides two calibration points on either side of the usual working value of pH5.5 to pH6.0. Note that modern research has shown the optimum pH value in hydroponics to be lower than the optimum for soil (usually pH6.0 to pH6.5)
On-demand dosers
These are used to automatically maintain the EC and pH at their respective set-points.
Most sensible recirculating hydroponic systems use a reservoir tank that has an automatic water make-up valve (ball cock). As the plants transpire, the water level in the tank falls and fresh water enters the system. This will tend to dilute the nutrient and may also have an effect on the pH. With an on-demand doser, the situation is continually corrected and the ideal EC and pH maintained at all times. This avoids the sudden shock associated with infrequent hand dosing.
Autogrow introduced the worlds first "timed dose" doser about 15 years ago (well, as far as we can tell). This gives a fixed size dose (user settable) when it detects that the EC is low and then waits for a few minutes (user settable) for the dose to mix-in before checking to see if another dose is needed. This method is extremely easy to set up and is not prone to overdosing like many other methods. For this reason other manufacturers are starting to copy the idea.
Many growers like to use a lower EC value during the heat of the day and raise it late afternoon through to the following morning. The new Autogrow NutriDose 1, as well as our greenhouse controllers, have two EC settings corresponding to two time zones to allow this to happen automatically. The NutriDose 1 can even add extra water to reduce the EC
During bright weather, plants grow strong with short internode spacing whereas in dull weather they tend to stretch and grow spindly. To compensate for this, growers will increase the EC during dull weather and lower it in bright weather. Some Autogrow greenhouse controllers will even do this function automatically, within limits specified by the grower.
So, this raises the question; can you exercise the same level of control as can be achieved with modern automatic doser?
Check out the NutriDose series or the mini-dosers for the home gardener
Labels: Autogrow Systems, Nutrient measurement and control, On-demand dosers, pH measurement
posted by seli at
10:45 PM
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IntelliDose
The intelligent hydroponic doser!
Works tirelessly to keep your nutrient tank in perfect balance.
Automatically adds nutrients and corrects pH as the plants feed.
Built-in USB – PC interface with USB cable and IntelliGrow software included.
Simple to operate – with AutoSet
Good looking and smart – the perfect companion for your nutrient tank
Up to 8 part nutrient dosing with variable ratios
Schedule to automate A:B:C:D etc ratio and EC changes
Feature packed
This hydroponic doser sets a new benchmark in the small dosing controller market. The Intelli-Dose is absolutely feature packed to enable it to cope with just about any hydroponic system. Just take a look at the specification overleaf.
Simple to operate
The secret to its simplicity is that the controller can be configured to suit various systems and when this is done all of the irrelevant settings disappear from the menus and PC screens. In addition to this, the controller can even be instructed to set itself up.
Knowledge is power
Once you have used the PC interface you will never go back to a controller without it. The reason is simple; you get to see all the settings in one list – no more fumbling around looking for a menu screen. You also get accurate logs of exactly what happened – you can see at a glance just what effect each dose is having and if anything starts to go wrong you will see it immediately. In addition, the PC can sound an alarm or even phone you if anything goes wrong.
Special functions
The controller can be set to operate with a different EC for day and night. Plants need weaker nutrient when they are transpiring in the heat of the day and stronger nutrient at cooler times. Now you can give them exactly what they need. An “add water output” can be used to reduce the EC as required. The irrigation output can be used to switch on an irrigation pump periodically to irrigate plants grown in pots. This can also have different settings for day/night.
AutoSet may be used to initially set the dosing timings. Just fill reservoir tank with plain water and stock tanks with regular solution – then select AutoSet. The system will perform a series of tests (by dosing and measuring the results) in order to automatically set the system dosing times.
For standard 2 part nutrients, proportional dosing may be selected so that it makes bigger doses when it is a long way from the setpoint and smaller doses as the setpoint is approached. A schedule can be entered that automatically adjusts the EC and even the nutrient ratios over the entirety of the plants growth. Now, how intelligent is that?
Features:-
8 outputs which can be freely allocated to nutrient dosing, pH lower and/or raise, irrigation and add water to lower EC
Nutrient measured in EC, CF or TDS (user selectable)
Temperature measured in oC or oF (user selectable)
Date format dd/mm/yy or mm/dd/yy (user selectable)
Doses up to 8 part nutrients (adjustable ratios)
Scheduling of nutrient ratios and EC - fully automatic changes every monday morning
Doses pH lower and/or pH raise
Autoset – automatically tests the system to choose best settings for dosing times and interval
Proportional dosing available for 1 and 2 part mixes (not suitable for 3 or more parts)
Possible to set different EC for day and night (avoid tip burn on lettuce etc)
Can raise EC (by dosing) or lower EC (by automatically adding extra water)
Three types of alarm independently selectable – local siren, PC sound card, phone alert via PC modem. All alarms can be independently disabled.
Irrigation pump output (or can be used for lighting control) programmed by time of day or time interval (different interval for day/night).
Fail safe dosing shut outs – stops dosing if probe failure detected or if it suspects incorrect settings.
USB cable and IntelliGrowTM PC software supplied for Windows 98, NT, 2000, XP. Supports up to two Intellidose controllers
Where to buy
In the USA contact American Hydroponics www.amhydro.com or phone 800.458.6543
In Western Australia contact Growth Technology www.growthtechnology.com.au +618 9331 3091
For the rest of Australia and New Zealand contact Autogrow direct www.autogrow.com +64 9 415 2380
Specification:-
8 outputs 24V DC
Nutrient measurement units EC, CF or TDS (EC x 500)
Measured range 0.00 to 9.99EC, 0.1 to 99.9CF, 0 to 1999 ppm
Nutrient resolution 0.01 mS/cm, 0.1 CF, xxx ppm
Nutrient measurement accuracy +/- 0.1 EC, 1.0 CF or 10ppm - temperature compensated
Nutrient dosing range 0.00 to 5.99EC, 0.1 to 59.9CF, 0 to 1190 ppm
pH resolution and accuracy – 0.1 pH
pH measurement range 2pH to 12pH
pH dosing range 5 to 7 pH
Nutrient and pH dosing times settable from 1 second to 30 seconds
Dosing interval settable from 0 minutes (continuous dosing) to 30 minutes
Dosing operates valves sequentially to reduce power surge
Temperature resolution and accuracy 1oC, 2oF
Temperature range 0-50oC, 32-125 oF
Operating temperature range 0-50oC, 32-125oF (and not in direct sunlight)
Power source – mains transformer pack supplied - 24VAC; specify mains voltage and pin type (power to controller can be between 12V and 24V either AC or DC)
Outputs will have the same voltage as the supplied voltage from the power pack. The supplied transformer is 24V AC and so the outputs will be 24V AC.
Large graphics display using simple four key interface (similar to cell phone key operation)
Nutrient sensor uses DiPulseTM technique to resist fouling
Dosing shut-off
- if nutrient is below 0.1EC, 1CF, 10ppm
- if pH below 4.5 or above 8.0
- if dosing effect is counterintuitive ie by dosing pH lower the measured pH goes up
- if sensor fault detected
Supplied with PC software and 5m USB cable
Can also be supplied with solenoid valve kit or peristaltic pump kit
Labels: Autogrow Systems, IntelliDose, NutriDose II b
posted by seli at
10:37 PM
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