How To: Connect the IMT Irradiance Sensor to eGauge

Installing the IMTIRR for use with the eGauge

Overview

Silicon solar irradiation sensors (Si sensors) offer an economical but robust and reliable solution for measuring solar irradiance levels, particularly for monitoring photovoltaic systems. The design of the sensor element, which corresponds to that of a photovoltaic module, make these sensors ideally suited as a reference for monitoring photovoltaic systems. The spectral sensitivity, which corresponds to that of photovoltaic modules, and the very similar incident angle modifier, enable a precise analysis of photovoltaic yields using measured values from the sensor.

Prerequisites

RS-485/USB converter for EG4xxx models or a RS-485 to Ethernet converter for EG3xxx models.

Instructions

Step 1: For best results, the IMTIRR Irradiance sensor must be installed in the same plane as the solar array. The sensor window should be clean and clear of any obstructions. Follow the mounting instructions included with the sensor, and contact IMT directly with any questions regarding unique installation environments.

Step 2: Follow the diagram below to wire the IMT sensor to your RS-485/USB converter.

IMT sensor connected to a 12Vdc power supply and RS485-USB adapter. The eGauge is not shown.

Step 3: Follow the steps below to configure the EG4xxx meter to read from the IMT sensor. As a supported device, the 3S-IS sensor has a predefined map built into the eGauge meter. This makes addressing and configuration very simple when using a RS485-USB adapter.

Configuration Steps

Step 1: From the main menu, navigate to Setup → Other Settings. Then, at the Left click on Installation.

Step 2: Under the "Remote Devices" section, click "Add Device" to add a new remote device.

Step 3: Enter a suitable device name. This field is arbitrary, but should make sense to the end user.

Step 4: Click the "Edit" button, and set the protocol to "Serial"

Step 5: Enter the device address. This will be modbus://imt_si.1@USBX where X is the USB port (1 or 2).

In this example the IMT sensor has Modbus address 1 and the RS485/USB converter is connected to USB port 1

Step 6: Click the gray ? next to the device address field. After a few seconds, this should turn into a green check mark.

Step 7: To save these settings, click the "Save" button at the bottom of the page.

Step 8: Add registers to the eGauge configuration from the remote device. For details please see: How to: Configure a Remote Modbus Device

Viewing Data

The data recorded from the IMT sensor can be viewed like any other data point recorded by the meter after completing the configuration steps in the section above . To see this data, navigate to the main graph page and select the appropriate register(s) from the list under the main graph. In the following example, the graph is set to display irradiance data (with temperature and windspeed data as options under the main graph.

Data from the IMT sensor can also be used in formula registers to calculate the estimated solar production at a site. The formula for this calculation requires real time irradiance and temperature data (obtained from the IMT sensor), the array's rating in watts, and the panel temperature coefficient (usually a small negative number). The following example shows this formula based on a 10kW array and a temperature coefficient of -.12%.

The formula field contains: P_PV($"Irradiance",$"Cell Temperature",10000,-.12)

Additional Sensors

The IMT sensor supports two optional additional sensors: a wind speed sensor and an ambient temperature sensor. These sensors connect directly to the IMT sensor body. To connect these sensors, remove the appropriate threaded cap from the sensor body (the wind speed sensor uses the two pin connector, and the ambient temperature sensor uses the three pin connector). In the image below, one cap has been removed (left).

When using an add-on sensor, the configuration is exactly the same except additional registers will need to be created to record data from the add-on sensors.

Do not connect anything besides official IMT add-on sensors to these ports. Doing so will cause damage and void the warranty on the IMT sensor.

Troubleshooting and Tips

Issue: When I try to configure the sensor, it does not resolve
- Check: If the remote device is timing out check that your wiring is correct and that there are no loose connections. Make sure the IMT sensor has power.
- Check: Check that your device address is correct. Be sure to use the correct Modbus address and USB port.