Temperature Measurement

This is for gardeners and growers that wish to utilize the best options for monitoring and troubleshooting the conditions in their grow area. Beginner and Intermediate level instruction and advice.

So if you like minutia, this may be for you.

1. Temperature Measurement for Home Gardeners
Indoor Gardens
Beginner & Intermediate Analysis
Jul 2013

2. Theory
•Temperature is a physical property.

•Measures the degree of heat in an object.
–The technique of measuring the changes in temperature was widely attributed to Galileo’s observations of wine levels at different conditions in 1592.

•Unstable and interferes with self.

•Standards of measurement are comparative at ‘sea-level’.

•Temperature is covered in many publications because it is a critical component of environmental conditions.

3. Application
•Temperature is one of the most measured parameters in the indoor garden.

•Following a defined schedule of measurement, and documenting readings is preferred.

•Liquid thermometers have been surpassed by digital detectors for some modern uses, however, old-fashioned liquid-in-glass remains a viable application.

•Obtain stability before reading and recording measurement.

•It takes time to do a fast test.

4. What Do You Want to Measure ?
•Air Temperature
Growing areas
–Ambient air.
•Fluid Temperatures
Reservoirs
•Hydration fluids
–Feeding and watering the plants.

•Solid Materials
Soil & Compost

That said, you’ll need to employ different equipment and techniques!

5. Equipment
•Digital
–RTD (Resistive Thermal Device)
internal workings above average.

•Liquid in Glass (LIG)
–Alcohol-filled Fahrenheit or Celsius w/ 1° subdivisions
–Metal casings (shown)

•Dial (not shown)

•NIST or NBS Standard thermometer is best because it is factory calibrated and certified.


•Tweakers: Do not take a reading from a pH, Conductivity, or TDS meter.

6. Thermometer Types
•Total Immersion LIG
–Entire unit must be completely immersed.

•Partial Immersion LIG
–Immerse to etched line.

•Digital and Dial
–Read while immersed.

7. Choosing the Range
•Choose LIG and dial thermometers that specify an approximate range of 50 – 200 F°

•Digital thermometers may have a wider range and still be accurate and precise.

•Tweakers: Don’t use a drugstore ‘people’ thermometer to take a measurement in these environments. If the measurement is important to your grow, purchase a quality instrument, and keep it in good condition.

8. Which Type Do I Use? Ambient Air
•A digital thermistor plugged into the controller.

•Digital probe immersed into a protected glass of water (or glycerin). Avoid hanging thermometer in air. Submerged thermometers are more accurate, though take a bit longer to reflect ambient conditions.

•A liquid in glass, either a total immersion or a partial immersion will work great. (H20, glycerine)

•Dial not recommended because the dial rolls around, and the face can be too hard to read without a magnifier.

•Tweakers: A digital or LIG Min-Max thermometer is available from Amazon or ebay for $20-30. Replace as needed.

9. Where Should Thermometer be placed?
To Measure Ambient Air
•Measured at the point-of-use.
–Near or at the top of the canopy, near fruits, flowers, or new growth.
–Anywhere ambient heat may accumulate, to evaluate removal, or modification.
–Do not place apparatus near walls, floor, or roof of grow area. These will yield biased results (i.e hang digital unit on wall, but place probe in point-of-use area).

–Tweakers: Do not measure in air. Always construct a place to maintain a beaker (tall shot glass, small juice glass) filled with water (RO, distilled, filtered). Do not use tap water. Cover glass with several layers of plastic and a rubber band. Poke a hole in the plastic no larger than the thermometer. Keep filled to the immersion line (digital probes in at least 1” water).

10. Which Type Do I Use? Reservoirs
•A digital probe may be fed into the tank and left there. Read as needed.

I don't run in hydro, so any advice here is welcome.

11. Where Should Thermometer be placed?
To Measure Reservoirs
–The point of use is where the fluid temperature is the most stable (you’ll have to test different areas).

–Avoid corners, outside walls, or intake/outake or high/low water level areas. Avoid the root ball if possible.

–Adhere to the normal tank (fluid) level to determine immersion depth.

12. Which Type Do I Use? Nutrition and Hydration Fluids
•Fluids used to feed and water the plants will respond the best to digital, or liquid in glass types.
•A dial thermometer may be used if it can be placed securely in container and left alone for 10 – 20 min.
•Here is a conundrum:
–Immerse thermometer (or probe) in the solution? Could cause contamination or crossover.
–OR pour a small amount out and then immerse thermometer or probe? Temps will fluctuate quickly making stability elusive.

13. Where Should Thermometer be placed?
To Nutrient and Water Solutions
–The point of use is where the fluid temperature is the most stable (you’ll have to test different areas).
–
–Avoid touching the sides or bottom of container.
–
–Adhere to the fluid’s natural level to determine immersion depth.

14. Which Type Do I Use?
Soil and Compost
•Dial (or Bi-metal) are the economical choice.
•If greater accuracy is needed, use digital.
•If time is not an issue, use LIG.

Tweakers: Do not expect stability when measuring in dry solids. The pockets of air will create fluctuations.

15. Units of Measurement
–Fahrenheit in °F, measures water freezing at 32 °F, and boiling at 212 °F

–Celsius in °C, measures water freezing at 0°C and boiling at 100°C.

Conversion Factor
°C x 9/5 + 32 = °F
(°F - 32) x 5/9 = °C

16. Procedure
•STEP 1: PREPARATION

– Equipment:
•Digital: Ensure thermometer is set to the correct units (°F or °C), and resolution (whole # or tenth). Thermometer should be cleaned prior to use.
•Battery replacements on hand
•LIG: Inspect for cracks, and fractures.
•Increment markings are clear.
•Dial: Usually no prep is needed.

–Paperwork:
•Bench sheet is handy.

17. Procedure
•STEP 2: IMMERSION

–Digital and Dial:
•1 inch is the standard depth, but several inches is acceptable.

–LIG:
•Either immerse to the depth indicator line, or within 1 inch of expected reading, or within 1 increment of the expected reading.


18. Procedure
•STEP 3: ANALYSIS

–Immerse to appropriate level.
–Wait for reading to stabilize
Digital should stabilize within seconds. Loook for an idicator on the display screen.
Dials should stabilize in less than a minute.
LIG may take minutes. Slow fluid movement is better. Fast movement contributes to fluid separations.
–Do not remove thermometer from sample until AFTER the measurement has been read.
–If LIG, read to closest increment, no guessing in between.
–Record the temperature.

19. Procedure
•STEP 4: DOCUMENTATION

–Read the measured result Add any correction factor.

–Record the adjusted result and unit.
•Farenheit, Celcius.


Tweakers: For troubleshooting purposes document abnormal conditions such extreme high or lows.


20. Calibration
•A thermometer may need to be calibrated periodically. If readings are suspect.

–Calibration is performed by submerging two thermometers together and noting the difference in readings.

–Replace thermometers that give inaccurate readings. (It happens)

21. Interferences
•Vibration causes friction and/or turbulence which will change the temperature.
–Do not stir during measurment.

•Physical damage to the thermometer will create inaccurate measurements.
–Replace all damaged equipment.

•Temperature variations may come from body heat, damaged equipment, and shallow depths or low volume.

22. Thermometer Storage
•Store digital instruments out of extreme heat, or cold, according to manufacturer’s instructions.
•
•Store liquid-in-glass (LIG) thermometers in a metal casing to avoid breakage.

•Store LIG’s upright to avoid fluid separations.
–Good use for all those mugs from the tude. Fill w perlite or vermiculite.

23. Trivia
•Avoid using infrared instruments unless you are planning on measuring the outside surface temp of a giant boiler.

24. Ice-Point Calibration
LIG & Digital
Ice-point is 32 F°, or 0 C°.

Fill a small Styrofoam cup with crushed ice.

Wear gloves (body salt and oils will interfere).

Add COLD water. There should be no air pockets.

Submerge thermometer to immersion line.


If the reading is not as stated above, the differnce must be added to all your readings.

Write it down

25. Ice-Point Calibration
Dial
Follow instructions for LIG calibration.

In the back of the dial, locate the small nut.

Use a small wrench to adjust the needle to 0 or 32 respectively.

Return to ice bath.

Repeat until the needle is stable at ice-point temperature.

Replace ice and water if it becomes slushy.

26. Methodology
Standard Methods, 20th Edition, 1998

•SM 2550B Temperature

•EPA Methodology

27. NIST
•NIST
–National Institute of Standards and Technology
•Certified reference thermometer
•Platinum Resistance thermometer


28. Where Can I Purchase a Quality Thermometer ?
•Amazon (Full Store Directory)
–Automotive & Industrial
•Lab & Scientific –or- Industrial & Scientific
–Test Measure & Inspect
»Pressure Gauges -or- Pressure and Temperature
- Temperatue and Pressure –or- Pressure
- Thermometers

Amazon keeps changing the name of the thread, so it can take a minute to find these. Check the menu above the pictures instead of the one on the left.

29. A Warning about Mercury
•While mercury-filled is the most accurate liquid-in-glass thermometer, the transportation, use, and disposal has made it obsolete for ordinary usage.

•Mercury is a hazardous substance, and carries the risk of human exposure, hazardous material spills, and fiduciary accountability.



From the author:
I have been involved with evaluating, purchasing, and troubleshooting thermometers for many years.
I wrote this article for training purposes.

Next: Hope to add pictures.

Enjoy, remark, ask questions.
aisach

Nice writeup, thanks for the treatise!

My pleasure. I hope this is one of many more to come.
Thanks

Unfortunately, I was unaware that there was a 72 hr time limit on editing posts. I am going to turn this into a journal so that I can edit it whenever I need to. Sorry about that, peeps. I really wanted to add pictures, and more info. Lesson learned!

Please feel free to contact me here if you have any questions, tho.

I have a detailed 4 part journal for temperature measurement.
For those that wish to know about equipment, calibration, etc, covering more than these posts.
With pictures.