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PLC interface board


My client designs and builds professional cooling installations and wanted a means to control a servo valve for flow regulation via dual PLC controllers. The outputs of the dual PLC had to be merged into one signal which is connected to the valve. The design is such that the PCB fits in a DIN rail mountable case for easy integration into equipment rack. There was a very tight deadline of just two weeks in which it was designed, tested and manufactured. It is installed in a cooling system for a livestock facility.


The output voltage is modulated (with PWM) according to the voltages applied at the inputs, it has three output stages. For every output stage it has a potentiometer to trim the output voltages. Although not specified in the design requirements, the LEDs where a simple afterthought to help the client with installation debugging. The firmware is written in C. It is carefully coded and checked, as it is controlling a critical component in the cooling system.


A3 Koel- en Vriestechniek BV


Sorry, this was a paying client project and the source files are not available for download.

Photo of custom PCB

Finished PCB

Photo of assembled controller

Finished product (Belimo is the brand name of the servo valve)

Photo of the controller in it's final place

On-site installation by client