Greetings,

I have a customer who had been using a 12-24 VDC power supply to power our wall mount Co2 sensor for a 0-5 VDC out put to their controller. Their controller is a Microzone II that uses 24 VAC to be powered. They kept popping the circuit breaker back at the panel, then they changed to a different power supply that was 12-24 VAC and all was well.

My question is this, I thought most controllers have bridge rectifiers built into the analog inputs, so you could connect a sensor device wich is being powered by either DC or AC? Keep in mind this Microzone does not source power you have to provide it as an external power supply.

 

Most logic controllers do not have bridge rectifiers built into analog inputs, in fact most of us would recoil in horror as it introduces non-linear elements into circuit. However as the Microzone II is only to 10bit accuracy, HVAC designs here was never going to be precise.

It appears to me the Microzone II is AC powered simply for convenience but functions internally on DC. This is suggested by the output designated 5.1v (20ma). Unfortunately it doesn't expressly state DC.

I would be more concerned that the Microzone II is powered from 24VAC (nominal) suggesting a floating isolated supply, and has no earth reference apart from Analog input/output and comms. link screens.

Consequently I would recommend powering the unit from nominal 24vDC and linking OvDC to earth.

 

I'm not aware of any PLC that has a rectifier on the front end of it's analog input, the analogs are normally 1-5 VDC or with a 250 Ohm resistor 4-20 mA DC

> My question is this, I thought most controllers have bridge
> rectifiers built into the analog inputs, so you could
> connect a sensor device wich is being powered by either DC or AC?