Infrared Radiometer FAQs

Why is my infrared sensor giving low or erratic readings?
Low or erratic readings are generally due to the sensor window becoming occluded with dirt or other organic deposits. You may want to perform a window cleaning to see if the readings improve. As a reference, when we get infrared sensors back for recalibration we first clean the sensors using a cotton swab dipped in water or a light acid, such as vinegar. The vinegar helps to dissolve calcium and salt deposits. Use the cotton swab to clean the inner threads and sensor window. Be careful not to apply too much pressure to the window, as it may actually scratch the anti-reflective coating. We then do a second cleaning to the sensor window using a solvent, such as acetone or ethanol. Many times, this will bring the sensor’s readings within specification. If not, then sending the sensor back for a recalibration may be necessary.
What resolution in microvolts is required to get precise readings?
SI-100 series radiometers have sensitivities in the microvolt range, approximately 20 to 60 µV per C difference between target and detector (depending on specific model). Thus, a compatible measurement device (e.g., datalogger or controller) should have resolution of at least 3 µV (0.003 mV), in order to produce temperature resolution of 0.05 C.
What field of view do I need for my application?
Field of View (FOV) is widely dependent on the application. Essentially, you want to select a FOV model that only “sees” what you want the temperature of. A simple FOV calculator for determining target dimensions based on infrared radiometer model, mounting height, and mounting angle, is available on the Apogee website and in the app store.
How often should I recalibrate the sensor?
It is recommended that infrared radiometers be recalibrated every two years. See Recalibration and Repairs for details regarding return of sensors for recalibration
Can I add additional cable to the sensor?
When sensor is connected to a measurement device with high input impedance, sensor output signals are not changed by shortening the cable or splicing on additional cable or splicing on additional cable in the field. Tests have shown that if the input impedance of the measurement device is 10 M or higher, there is negligible effect on the radiometer calibration, even after adding up to 50 m of cable. Apogee model SI series infrared radiometers use shielded, twisted pair cable, which minimizes electromagnetic interference. This is particularly important for long lead lengths in electromagnetically noisy environments. For information on how to make a weatherproof cable splice click here

We offer custom cable lengths of our high quality cable and splice kits that can be ordered at the time of purchase or at a later date.

How can I use a voltmeter to verify my sensor is working?
The radiation detector in Apogee SI-100 series infrared radiometers is a self-powered device that outputs a voltage signal proportional to the radiation balance between the detector and target surface. A quick and easy check of detector functionality can be accomplished using a voltmeter with microvolt (µV) resolution. Connect the positive lead of the voltmeter to the red wire from the sensor and the negative lead (or common) to the black wire from the sensor. Direct the sensor toward a surface with a temperature significantly different than the detector. The µV signal will be negative if the surface is colder than the detector and positive if the surface is warmer than the detector.
How can I use a voltmeter to determine readings from my infrared radiometer sensor?
The SI series is considered to be self-powered with each sensor having custom calibration coefficients. Average sensitivities are 60 (SI-111), 40 (SI-121), 20 (SI-131), and 50 (SI-1H1) μV C-1. A voltmeter that can resolve the given sensitivities is required. A high resolution ohmmeter will also be needed to measure the thermistor's resistance. After the mV response and thermistor resistance are measured, they will need to be combined with the custom calibration coefficients to produce the given target temperature. Calculation details and equations are available in the sensor manual. To learn more, click here for a knowledge base article on how to take IRR temperature measurements without a datalogger.
How do I get data off my meter?
Handheld Meter Video Guide
The AC-100 communication cable is used to download saved measurements from any of our handheld meters. This USB cable includes a built-in circuit board to convert voltage levels to be compatible with the meters-normal USB cables will not work. The AC-100 also comes with a flash drive that includes the necessary computer software, drivers, and instructions. If you already have the AC-100 and just need the software files please click here.
Do I need to order a sensor to go with my meter?
No. All Apogee meters (MO, MP, MQ, and MU series) either have sensors built into the meter or attached via two meters of cable. If you order a sensor only (SI, SO, SP, SQ, and SU series) you will need to have your own datalogger (or, depending on the sensor, a voltmeter) to collect information from the sensor.
Can I add cable to my meter?
Although it is possible to splice additional cable to the separate sensor, note that the cable wires are soldered directly into the circuit board of the meter. Care should be taken to remove the back panel of the meter in order to access the board and splice on the additional cable, otherwise two splices would need to be made between the meter and sensor head. Click here for further details on how to extend sensor cable length.
I received an error code on my meter. How do I fix it?
Error codes will appear in place of the real-time reading on the LCD display and will continue to flash until the problem is corrected. For steps on completing a fix please refer to the manual.
Err 1: Battery voltage out of range. Fix: replace CR2320 battery and perform master reset.
Err 2: Sensor voltage out of range. Fix: perform master reset.
Err 3: Not calibrated. Fix: perform master reset.
Err 4: CPU voltage below minimum. Fix: replace CR2320 battery and perform master reset.
What kind of battery does my meter take?
The meter takes a CR2320 coin cell battery.
What should I do if my meter becomes non-responsive or experience anomalies?
A master reset can be performed that may correct the problem. *Note: a master reset will erase all logged measurements from memory.

First press the power button so that the LCD display is activated. While still powered, slide the battery out of the holder, which will cause the LCD display to fade out. After a few seconds slide the battery back into the holder. The LCD display will flash all segments and then show a revision number. This indicates the master reset was performed and the display should return to normal.

Is each logged or sampled reading time stamped?
No – user should record the starting time when the meter is placed in LOG mode and take note of time when sampled readings are taken.
How many readings will the meter take in LOG mode?
When in LOG mode the meter will power on/off to make a measurement every 30 seconds. Every 30 minutes the meter will average the sixty 30 second measurements and record the averaged value to memory. The meter can store up to 99 averages and will start to overwrite the oldest measurement once there are 99 measurements. Every 48 averaged measurements (making a 24 hour period), the meter will also store 99 integrated daily totals in moles per meter squared per day (mol m-2 d-1).
How many measurements can I take in SMPL mode?
When in SMPL mode press the sample button to record up to 99 manual measurements (a counter in the upper right hand corner of the LCD display indicates the total number of saved measurements).