Know a quick and dirty way to convert a 4-20ma to a discrete 24vdc sink input?

[OkiePC]

Nice! No pricing information, though.

It says no setup or configuration required and only has one NO contact. So does it close any time the input signal is valid, is it set to a certain specific value or what? I see no knobs on it either.

The WICI stuff is solid as a rock and their customer support is very good, so yes, more money.

 

[I_Automation]

I have used PR Electronics 4116 signal conditioners with a programmable relay output for exactly this, and also to convert a few TTL signals to 24V.


On the TTL I had to add a card to a full SLC rack, the TTL input card only had 3 used inputs and there were plenty of unused 24V inputs. Set the signal conditioners to 0-5V in, and since the analog out wasn't used set it to voltage to not get a mA loop fault, then programmed the relay outputs to activate at 3V or higher for the 3.3V TTL signal.


EDIT: Since it's only one input any change you have a micro-PLC with an analog input somewhere (or eBay) and program that to activate an output above a certain mA level?

 

[I_Automation]

It says no setup or configuration required and only has one NO contact. So does it close any time the input signal is valid, is it set to a certain specific value or what?

When ordered it is configured to a specific setpoint, like those new thermostats you can get set to 72°F no matter what you think you may want in your building.

 

[JLand]

I know this was a false alarm, but just for future knowledge, is there a general rule of thumb for a minimum voltage to be considered a true input on a DI card? Knowing this would be handy, as that'd be how you'd pick the right resistor to convert from mA analog input to a 24VDC digital input.

If I had to do this in reality, I suppose the best solution would be to simulate the current at the device (if possible) and use a pot to determine the true value of the resistor to use.

 

[I_Automation]

I know this was a false alarm, but just for future knowledge, is there a general rule of thumb for a minimum voltage to be considered a true input on a DI card? Knowing this would be handy, as that'd be how you'd pick the right resistor to convert from mA analog input to a 24VDC digital input.

If I had to do this in reality, I suppose the best solution would be to simulate the current at the device (if possible) and use a pot to determine the true value of the resistor to use.

That depends on the brand and the specific card.


I have seen DC input cards rated with voltages of 9, 10.5, 12, 16, 18 and 23V. I started checking this for a 12V vehicle application and I wouldn't use a 12V minimum input on a 12V system - if the voltage dropped to 11.8 the result might be sporadic.



Even the input listed as 23V minimum might have problems if the power supply was taken down a couple volts. I have been in panels where the 24V was actually 21 with everything added over the years and not upgrading the power supply.