Frequently Asked Questions
- ACCUPAR LP-80 What leaf distribution, chi, value should I use for trees? If you set x (chi) to 1, then that covers almost all of the real vegetation cases.One of our scientists prepared an application note that describes the reasoning for this. Read it here.
- SC-1 Leaf Porometer - PHYTOS Can the SC-1 be used with needles/ thin leaves? When measuring small needles or leaves, they should be inserted into the sensor as shown below. This is because single needles or small leaves (including blades of grass) may not adequately cover the aperture of the sensor.For an accurate measurement it is critical that the entire cross sectional area of the diffusion path be covered with leaf material. Sometimes it is necessary to remove the leaves/needles from the plant in order to arrange them over the opening in the diffusion path. This results in an accurate measurement as long as the measurement is completed within two minutes of leaf/needle removal, because the stomatal aperture should remain unchanged for at least that long after disturbance.Please note that needles with a square or triangular cross-section and lots of sclerenchyma may not work with the SC-1 because they will prevent a good seal with the chamber. Needles of the genus Picea are a good example of needles for which the SC-1 is not well suited, while the flat, pliant needles common to Abies work quite well.
- ACCUPAR LP-80 - PHYTOS How can LP-80 data be used?
- Computing crop coefficients => irrigation management
- Modeling biomass production
- Leaf area index (LAI), a measure of the foliage in a canopy
- ACCUPAR LP-80 - PHYTOS How can crop coefficients be computed from data collected with the LP-80? Crop coefficients are used to estimate crop water needs. The procedure for computing a crop coefficient for a vineyard using the AccuPAR LP-80 and Williams (2001) correlation is as follows:
*Interception is computed as 1 – t, where t, the fractional transmission, is the ratio of one or more measurements below the canopy to one or more measurements above.For more information read: How to use PAR for more efficient irrigation
- Make measurements on a clear day within a couple of hours of noon.
- Make one PAR measurement above the canopy and several equally spaced measurements below the canopy from row center to row center following the instructions in the AccuPAR manual.
- Don’t sample preferentially in sun or shade areas, and take enough samples to give a good average for the area.
- The AccuPAR automatically computes t*. Subtract this value from 1.0 to get the interception. Williams’ (2001) correlation multiplies this value by 1.7 to get Kc (crop coefficient). For example, if t were 0.60, interception would be 1 – 0.60 = 0.40, and then Kc would be 1.7 x 0.40 = 0.68.
- ACCUPAR LP-80 - PHYTOS Is there a lower limit of “above PAR” to collect reliable data with the LP-80?
There isn’t a lower limit of “above PAR” to collect reliable LAI data; however, very large zenith angles around dawn and dusk can cause more variability. As long as sampling does not occur within an hour of dawn and dusk, the data collected are reliable (even 300 µmol m−2 s −1 on a diffuse day). Most peer-reviewed research would prefer sampling with the LP-80 between 10 am and 2 pm.
- SC-1 Leaf Porometer - PHYTOS How long does a measurement take? One measurement with the SC-1 takes 30 seconds (in auto mode). The time to get the relative humidity <10% between measurements varies (e.g., 30-90 seconds), but it shouldn’t take longer than 90 seconds of shaking the sensor head. If it takes longer than 90 seconds of shaking the sensor head between measurements, then check the desiccant to ensure it is blue (for Indicating Drierite, 10-20 mesh). If the problem persists, replace the teflon filter that separates the measurement chamber from the desiccant, and check the rubber seals on the porometer head.
- SC-1 Leaf Porometer What should I check if during the measurement period, leaf conductance declines toward zero instead of increases (as it would normally over the auto measurement period)?
Double check that the units in the measurement screen are in mmol/m2s and not m2s/mmol or s/m?
- SC-1 Leaf Porometer - PHYTOS Can the diffusion path of the SC-1 be horizontal, if I take the clamp off to take measurements (i.e., measuring fruit and tree trunks)?
This is not a good idea if the bead is in the diffusion path. The bead needs to be sitting down against the porous plastic membrane (Teflon disc) that retains the desiccant. If not, it could violate the assumption of 1-D vapor diffusion between the two vapor pressure sensors. That diffusion path doesn’t have to be perfectly vertical, but it needs to be vertical enough to ensure the bead is out of the way.
- SC-1 Leaf Porometer - PHYTOS Can silica gel be used as desiccant in place of the Drierite, for the leaf porometer sensor head? Silica gel works. It doesn’t last as long or scrub down as fast as the Drierite. You can use silica gel in place of the Drierite desiccant, but be prepared to need to change the silica gel more often and expect possibly longer shake down times. Non-indicating Drierite can also be used. It is safe and should work just as well as the indicating Drierite. Use 10-20 mesh size.
- SC-1 Leaf Porometer How often should the SC-1 be calibrated when taking readings out in the field? Verify the measurement accuracy daily or after a change in field conditions. This is done by using the calibration plate and moist filter paper. Recalibrate when the measurement falls outside of the expected range. When calibrating in the field, wind gusts can dry out the filter paper faster, so try to perform the calibration in a sheltered area from wind. Use the SC-1 case to protect the calibration plate from drying out fast, and also turn the calibration plate upside down between calibration points, so it doesn’t dry out as quickly. As long as you have fresh desiccant and have performed any necessary maintenance, then you should expect the SC-1 system to calibrate in a stable environment. If you put the sensor head on a different SC-1 handheld, then recalibration is required. The reason is that the calibration for the sensor head is stored in the hand-held device.
- SC-1 Leaf Porometer - PHYTOS What type of calibration filter paper should be used for the SC-1?
Use Whatman #3 filter paper and use a hole punch to make the correct-sized discs. If you use a different type of filter paper, then verify with the Whatman #3 that the substitute filter paper gives the same expected results.
- ATMOS 14 - SRS - IRT - ECT - PAR - PYR - ATMOS 22 - ATMOS 41 - PHYTOS 31 - ECRN-100 - ECRN-50 How do I assemble the anemometer mast?
The anemometer mast is suitable to mount METER’s above-ground sensors: ATMOS 41, ATMOS 22, ATMOS 14, PAR, PYR, IRT, SRS, PHYTOS 31, ECRN-100, ECRN-50, and ECT. Additional brackets may be required for some products.
Anemometer mast kit: 1 extendable mast (fiberglass), 1 guy ring, 1 guy rope (7.6 m nylon rope), 3 guy rope anchors, and 1 mast base with center peg and set screw.
Mast diameter: 4.5 cm
Mast adjustable length: 1.3 to 2.3 m
Tools to bring to the field: measuring tape, long metal screwdriver, mallet, wrench, level, scissors, optional shovel, and lighter.
Installation: Position the mast base in the desired installation location, avoiding large rocks. Install the center peg using a mallet. Insert the mast into the base so that the center peg is inside the mast tube. With the mast in the base, turn the set screw so it is hand-tight against the mast. Then, gently turn the set screw with a wrench. Do not over tighten or the fiberglass pole will break. Put the guy ring over the extendable mast. Cut the guy rope into thirds (approximately 2.5 m each) and burn the ends with a lighter to prevent fraying. Position the rope anchors equidistant apart to be about 1 meter away from the mast. Screw the anchors into the soil at the same angle as the guy rope using a long metal screwdriver as a make-shift turning handle. Attach the guy rope to the guy ring in 3 equidistant holes (show below) using knots. Then knot each guy rope in the corresponding anchor. Pull the rope very tight and ensure the mast is level and straight.
Once the mast is secure, move the adjustable lever up to release the extendable mast. Move the lever down to secure the mast to the correct height. Install instruments following the sensor quick start guides and manuals.
Limitations: Rocky soils, long-term monitoring sites, locations with high animal traffic. The SRS extension arm may be too heavy for the fiberglass mast.
- ACCUPAR LP-80 How often should the LP-80 be calibrated? METER recommends performing the user calibration routinely on a weekly basis. It is a fast and easy routine and only takes a couple of minutes. Refer to Is it time to recalibrate your ACCUPAR LP-80 external quantum sensor?
- ACCUPAR LP-80 I took my readings, but I’m still getting LAI value of 0.0. What’s going on? 1. Make sure that the location (latitude and longitude), date, and time are entered correctly in the AccuPAR LP-80 handheld.2. Perform the user calibration on a clear and sunny day with the light bar level and green cap removed from the external PAR sensor. Ensure that the external PAR sensor is connected and level. The user calibration should be performed in an open area, where there are no shadows on the sensors.3. Read the measurement tips in the LP-80 user manual.4. Contact METER if you have additional problems.
- ACCUPAR LP-80 Can we add more locations (cities) to the hand-held options for setting the latitude/longitude?
The cities are there to at least provide an approximate location to start from, and then you make adjustments from there. Select the closest city, then just use the up and down arrows to move to the Latitude and Longitude lines. Press “ENTER” to make adjustments to these values to better reflect the actual location. Once it is set correctly, they just press the MENU button again to get out of this menu and the setting will be saved.
- PHYTOS 31 How often should I recondition the surface of the PHYTOS 31 leaf wetness sensor to prevent UV damage?
METER recommends applying McNett UV Tech to the PHYTOS 31 sensor every 45 days. McNett UV Tech is sold separately and is the only 3rd party tested and approved UV blocking system for the PHYTOS 31.
- PHYTOS 31 Can I measure the presence of rain, fog and dew with the PHYTOS 31 leaf wetness sensor? Yes, depending on the situation, you can use the PHYTOS 31 as a rain detector using the following methods:Other methods to measure/detect fog and dew with the PHYTOS 31 are described here:
- PHYTOS 31 What is the accuracy or tolerance of the PHYTOS 31 (LWS)?
We set each PHYTOS 31 (LWS) to read very close to identically when dry. Our specification is 318-321 mV at 3000 mV excitation. The sensor does not have a voltage regulator, so larger differences could be caused from an unstable excitation voltage. Because the sensor is not regulated, the output will be somewhat proportional to the excitation (2.5 to 5.0 V).
- SC-1 Leaf Porometer What should I do if the SC-1 will not connect to a computer using the cable adapter?
- SC-1 Leaf Porometer Where can I purchase new desiccant?
The desiccant is Drierite 10 to 20 mesh. You can purchase new desiccant from METER or another supplier.
- SC-1 Leaf Porometer What should I do if the SC-1 calibration is abnormally slow (1+ hours) and the calibration is unsuccessful after multiple attempts? 1. Set the instrument and calibration supplies in measurement environment before calibrating for 10+ minutes. Replace desiccant and follow the calibration instructions in the SC-1 Calibration quick start.2. If unsuccessful, replace Teflon filter and then try calibrating.3. If unsuccessful still, conduct cleaning and maintenance shown in the maintenance video, and then try calibrating.5. If unsuccessful still, contact METER for further troubleshooting or to request an RMA to send it in for repairs.
- SC-1 Leaf Porometer How do I convert between conductance and resistance units?
Refer to the excel spreadsheet that can be downloaded here. The spreadsheet was provided by a METER scientist.
- SC-1 Leaf Porometer I get the message “initial conductance too high” before I take a measurement. Is that normal, and what could be the cause? The SC-1 will give you the message “initial conductance too high” between every reading. This is normal operation of the sensor. The sensor head needs approximately 30 seconds to 1.5 minutes of shaking to return to a state where it can begin another reading. It is not a problem but part of the design of the sensor. The chamber must have an RH below 10%, and the stomatal conductance must be 0 to clear the message “initial conductance too high”. When you receive that message, the stomatal conductance is not yet 0, and you must continue shaking the sensor head to equilibrate the chamber. Refer to the SC-1 quick start, SC-1 Calibration quick start, and SC-1 calibration video for operating instructions.
- SC-1 Leaf Porometer How do I put the spring back in after doing maintenance on the porometer?
Position the spring in the sensor head as shown in the pictures. Then, insert the pin to secure the spring.
- SC-1 Leaf Porometer Do I need to put a bead in my new leaf porometer?
You do not need to replace the bead unless the screen and bead fall out. You should have spare screens in your porometer kit. Watch our maintenance video, and it will walk you through reassembling your sensor head with the proper bead and screen placement.
- SC-1 Leaf Porometer Why does the SC-1 sensor head and diffusion path need to be vertical when taking measurements?
If the bead is in the diffusion path, it needs to be sitting down against the porous plastic membrane that retains the desiccant. If not, it could violate the assumption of 1-D vapor diffusion between the two vapor pressure sensors. That diffusion path doesn’t have to be perfectly vertical, but it needs to be vertical enough to ensure the bead is out of the way.
- SC-1 Leaf Porometer - PHYTOS Can the SC-1 provide accurate leaf temperature data?
While the leaf and sensor head come into thermal equilibrium quickly, the temperature reported by the sensor may not be a good proxy for the leaf temperature in equilibrium with the environment. The clip most likely warms the leaf slightly when the clip is placed on the leaf. This is not important for the reading of stomatal conductance because all that matters there is that the leaf and chamber are the same temperature. But it does matter if you want to use that reading to calculate transpiration. I recommend using an infrared thermometer to get a leaf temperature before placing the sensor head on the leaf for the best leaf temperature measurement.
- SC-1 Leaf Porometer - ATMOS Why doesn’t the Leaf Porometer output transpiration like the LI-COR used to?
The SC-1 Leaf Porometer measures the vapor flux to arrive at stomatal conductance, which on the surface gives you leaf level transpiration. However, the leaf chamber of the SC-1 forces its own environment on the leaf, so the chamber steady-state transpiration will likely differ significantly from the environment steady-state transpiration. This is fine for stomatal conductance since the reading is taken within 30 seconds, but it doesn’t work for transpiration. We recommend you use independent atmospheric vapor pressure and leaf temperature measurements coupled with an estimate of leaf boundary layer conductance to calculate transpiration from the stomatal conductance measurement made with the SC-1.