Silicon Irradiance Sensors:


1. Why should I use a Silicon Irradiance Sensor instead of a pyranometer to monitor irradiance levels at my solar array?

a. Because a Silicon Irradiance Sensor is made of the same material as your array and is mounted in the same “plane” as the array, it will give a much more accurate reading of solar irradiance levels reaching your solar modules, considering all factors such as angle of incidence, reflected light, etc. A pyranometer, particularly one mounted simply in a horizontal plane, is going to give a reading of all absorbed irradiance, including that reflected from nearby surfaces.

2. How long has IMT SOLAR been manufacturing Silicon Irradiance Sensors?

a. Our partners in Germany, IMT GmbH, have been designing and manufacturing Silicon Irradiance Sensors since 1993.  Because of our experience and a well thought out design process there are over 18,000 of our sensors installed around the world – including many from the earliest days of manufacturing.

3. What is the IP rating of our Silicon Irradiance Sensors?

The traditional style sensor (SI- Standard) has an overall rating of IP65 with a cable gland rating of IP67.


4. What is the best mounting position for the silicon irradiance sensors?

a. The sensors should be mounted at the same tilt angle as the array (same “plane” as the array.)

5. The temperature output signal on the Si-420TC-T (4-20mA) sensor is listed on the data sheet as  13.88 + 0.08/deg.C x T (deg.C). What exactly does this scale to at my 4-20mA analog input channel?

a. The scaling range is -123.5 deg.C  to +76.5 deg. C (i.e.  4mA = -123.5 deg.C  and 20mA = +76.5 deg.C)

6. The temperature output signal on the Si-13TC-T (0-10VDC) sensor is listed on the data sheet as  2.268V+86.9mV/°C*T (deg.C). What exactly does this scale to at my 0-10V analog input channel on my data logger or SCADA system?

a. The scaling range is -26°C  to +89°C (i.e.  0V = -26°C  and 10V = +89°C)

7. The Si-01TC…series of irradiance sensors looks like it only goes to 1000 watts per sq. meter of irradiance. We need to be able to measure irradiance levels higher than that. Is that possible?

a. All of our silicon irradiance sensors will measure to 1500 watts/sq. meter. Specifically to the Si-01TC family, there are three ways to make higher readings as follows:

i. We can reconfigure the units before shipping for any range between 0-1500 W/sq m at 0 – 1V at the plant before shipping. There would be an additional charge for this however.

ii. Our Si-01TC sensors do not stop outputting at 1V. So if your datalogger analog input can go higher, to say 2V, then you will continue to see irradiance levels increase beyond 1000 at 1V at the same scaled rate.

iii. If your data logger input can only go to 1V, then a simple voltage divider circuit, using two precision resistors, can be installed right at the input to your data logger to get an accurate measurement of just over 1200 at 1V.

8. The IMT digital silicon irradiance sensor has an output that is RS485 communications. Does this RS485 channel include a Modbus protocol as an option?

a. Yes! We introduced the embedded Modbus RTU protocol in the summer of 2010 and this digital sensor has quickly become one of our most popular models.

9. What is the color coding on the IMT irradiance sensors with the cable pre-installed?

Irradiance: Orange

Power Supply (Plus): Red

Power Supply / Signal (Minus):  Black

Temperature:  Brown; only versions with „-T“

Shield:    Black (bigger diameter)