IMT Weather Station (Si-RS485TC-2T-v-MB)


The IMT Weather Station model Si-RS485TC-2T-v-MB (referred to as the IMT sensor for the remainder of this article) is a high accuracy irradiance and cell temperature sensor. Optional attachments can be connected to monitor windspeed and ambient temperature. The IMT sensor is resold (not manufactured) and supported by eGauge Systems for use in applications where measuring irradiance may prove useful. The most common application would be to estimate solar production for an array of a given size using the irradiance and temperature data from the IMT sensor.

There are several IMT models available. Only the Si-RS485TC-2T-v-MB is directly supported for use with the eGauge.

The IMT sensor communicates via Modbus RTU (RS485). A RS485 to USB adapter is required for use with the EG4xxx meter line, and a serial to Ethernet adapter is required for use with EG30xx meters. Instructions for using both adapters are included in this document.

A serial to Ethernet adapter may be used with the EG4xxx meter line, but this is not recommended.

If using multiple IMT weather stations on the same serial bus, the Modbus address must be changed. See the manufacturer's information at under "Software Si-Series" for more information.

Third party adapters may cause issues and are not supported. 

OEM Data Sheets

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Hardware Included

Installation and Wiring

For best results, the IMT 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 IMT sensor, and contact IMT directly with any questions regarding unique installation environments.

The IMT sensor has four wires and a heavier gauge wire shield connector. Depending on the application, the wire shield may or may not be used, and it is not shown in the following diagrams. If required, the wire shield should be connected to earth ground, not the RS485 ground or signal ground. Note that proper wiring is essential. Failure to wire the IMT sensor correctly will prevent the sensor from functioning and may cause damage.

Wiring for EG4xxx with RS485-USB adapter

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


The wire assignments are as follows:

Black: Negative side of 12Vdc power supply
Red: Positive side of 12Vdc power supply
Orange: D- terminal on RS485-USB adapter
Brown: D+ terminal on RS485-USB adapter

The larger, thick black wire is a grounded shield and must not be connected to the eGauge, power supply or USB485 converter. Only connect this wire if you know what you are doing as improper grounding conditions can cause damage or communication issues.

Additionally, it is necessary to connect the ground (⏚) terminal on the RS485-USB adapter to the negative terminal of the 12Vdc power supply. 

A barrel connector with terminal blocks is included with the IMT sensor. Use the female side to quickly connect the IMT sensor to the 12Vdc power supply without splicing any wires. The male side can be discarded or saved for use in another project.