0-10 VDC signal to 4-20 mA?

@danw converter is tested as seen in the photos, giving a bit more than 4mA and 10VDC over the open contacts.

Also a 0-10VDC converter to mA is a bit trickier than the other way around, my attempt to Google it gave more options from mA to VDC than other way around, unless it were complex structures including op amps.

I have a variable power supply and I'll get back to your question about V to mA conversion of the converter. (Might take two days until I have time though)

@4X4 yes I would also rather have the correct equipment installed but as this is installed here by an external company on the ship I want to try to make it work; of the only solution is to change the sensor to a 4-20mA or install a different converter then I'll order the right stuff which will take a while before it reaches me.

@genius the signal from the PT is 0-10VDC, I can measure it and share a photo if you like. The converter however can take either VDC -> mA or mA -> mA.

@parky I have tried to power the converter with the power delivered by the 4-20mA input of the PLC, unless if you have a different idea of connecting it other than series with the signal, I have had no luck. Also thanks for the link! I'll look into it ASAP.

@bryang the signal is not referenced to the ground, however, what you say about the loop being powered by either the PLC or the transmitter and not both, is exactly the problem, it's powered by both. I have another PLC to which I can try to connect it (I'll get back with details and pictures), if in this PLC does not power the loop, I might get it to work.

I honestly appreciate this kind of feedback, the wonderful thing about forums

Vincenturion said:

@bryang, what you say about the loop being powered by either the PLC or the transmitter and not both, is exactly the problem, it's powered by both.

Click to expand...

Yes, exactly the problem

If
- your analog input really, truly is an active, sourcing DC power AI AND you can not disable that DC power function

AND (boolean logic here)

- your voltage to current converter is actually an 'active', sourcing, 4-20mA output,

then, you cannot make the equipment function correctly.

There are commercial signal coverters with passive 'sinking' 4-20mA outputs. Here's an example of one.

This signal converter has
- DC voltage input
- 4-20mA output
" . . . a mA output can be selectively wired for sinking or sourcing." (sinking output is what you need for use with that AI if it is truly a sourcing AI)
https://api-usa.com/pdf/api/apd4300.pdf

There are other brands, as well.

@danw

Yes! Yesyesyes! Exactly what I need! It would be current sourcing output as the PLC module has 20VDC over it's mA input contacts and would therefore power the output of the DC to DC transmitter. The 24VDC power supply will then only be used for powering the pressure transducer.

My suspicion of having the wrong converter installed was right, however, thanks to (all of) you now I know why and I can tell my superintendent what I need to make it work and why I need it. Besides the fact that this solves a long ongoing issue at work it also expands my knowledge. Thanks a lot! Probably it'll take a while before I have the correct converter on board and installed (I'm guessing 8 weeks), at least I have good faith it'll finally work!

Vincenturion said:

It would be current sourcing output as the PLC module has 20VDC over it's mA input contacts and would therefore power the output of the DC to DC transmitter. The 24VDC power supply will then only be used for powering the pressure transducer.

My suspicion of having the wrong converter installed was right,

Click to expand...

Not quite. The converter must be have a passive, loop powered, current sinking 4-20mA output, powered by the DC power at the PLC input (assuming that PLC input is truly an 'active, sourcing input').

Right now, your existing converter module appears to be a powered, active, sourcing output and it will not work with a powered active, sourcing input.

Active (powered), sourcing outputs are matched with passive inputs (analog inputs do not actually sink current).

Passive, sinking outputs are matched with active (powered), sourcing inputs.

That statement, "It would be current sourcing output as the PLC module has 20VDC" should be, "It would be current sinking output [on the converter] as the PLC module has 20VDC [to power the output].

Ah right, my apologies, I mixed up the two. So current sourcing output would mean that the module powers the loop and current sinking is that the output is unpowered, right? So in my case I need a module with current sinking; which has an unpowered 4-20mA output.

I mixed up the terms 'sourcing' and 'sinking' (as they're new to me) but now I get it. Sourcing is powered and sinking is unpowered. Sourcing input + sinking output OR sinking input + sourcing output. Thanks for the clarification! If I seem repetitive it's only to make sure I got it right this time.

You got it.


The more common terms are active and passive
active = powered = sourcing

passive = unpowered = sinking


Sinking and sourcing are routinely used with discrete I/O.

Active and passive are more commonly used with analog I/O, but one has to go with the flow and the vendor spec sheet used sinking/sourcing.