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Opto 22

1. Digital Inputs

1.1. Frequency Input from Open Collector

Here's an example for wiring a GF Signet 2551 blind magmeter's frequency output (open collector style) to an Opto 22 IDC5 module.

The GF Signet 2551 open collector output works from +5 to +24 VDC.  Use +24 VDC to be well within the Opto 22 IDC5 input range (+10 to +32 VDC).


Install an isolated +24 VDC power supply.  Wire  + and – to terminals 1 & 3 on the 2551 as shown.  Add a 10 k-Ohm resistor (1/2 watt will suffice) between terminals 1 & 2.  Wire the 2551’s Frequency Out to the + side of the IDC5 and the 24 VDC power supply’s negative to the minus side of the IDC5. 


Note that the IDC5 has a theoretical max frequency measuring capability of 100 Hz, probably lower in reality (I can’t find the specs).  If the flow measurement frequency exceeds 100 Hz we should look at the Opto 22 IDC5B  (which of course would require a different power supply, nominally 12 VDC)





Polarity for the IDC5 module




Note this can also be applied to other I/O platforms and other flowmeters with open collector outputs, e.g. GF Signet.  This method is not applicable for the sine wave frequency outputs of some flow meters, especially ones that are amplitude based.

Compatible flow meters per 41st edition GF Signet Measurement and Control Product Catalog:  2000, 2100, 2507, 2536, 2537, 2540, 2551, 2552

In RCK's experience this has worked for 2536, 2537 and 2551 flow meters.