MC3 Ratiometric/regulated Sensors

Kevin 8 years ago in IQANdesign updated by Gustav Widén (System support) 8 years ago 1

We are looking at some sensors for a particular project and have the option for 3 wire ratio metric (4.75-5.25) or 3 wire regulated (10-30Vdc). Both sensors output voltage signals with a range of 0.5-4.5 suitable for the MC3 VIN. Is there any benefit of using a particular type when using for part of a safety system?

If we use ratio metric sensors, does the MC3 automatically offset the signal it receives from the sensor if the VREF drifts away from 5000mv? My guess is when we select reference voltage that ensures it becomes offset correctly automatically?

MC3 manual states ideally 5V sensors should be used with the VREF supply from the module unless its offset by other means when using external supply. Is this is because some engineers may use a separate 5V supply external to the MC3 and it could drift unknowingly which would ultimately affect the VIN signal and could cause a false signal because of a power supply issue? Im assuming this would not be an issue if we use regulated 8-30V sensors with a non ratio metric output?

With a radiometric sensor, absolute errors in the IQAN-MC3 internal 5V gets cancelled out, since both the VREF and the VIN:s follow this. In the IQAN-MC3 manual, you can see this as a difference in accuracy.

When comparing the two sensors, I would guess that the ratiometric sensor might have a slightly longer MTTFd than the sensor with 10-30 V supply, this is the other advantage I can see. The expected difference in sensor MTTFd should be since the 10-30 V version must be designed with more components, and drift faults in the sensor power supply should be counted as dangerous failures. If these are detectable will depend on either sensor self-tests, or a second independent channel that you can compare it to in your application.

In the case of using IQAN-MC3 VREF, you will know that you have a monitored sensor supply.