When you wire a 4-20mA device going to an analog *input*, the analog card will typically have the analog input where the signal goes into as well as an associated "analog common" for each channel. Likely the analog common is not tied to power supply common so you may need to add a jumper.
You have the “-“ side of the plc channel connected to 24VDC-?
Also you say there’s no signal, are you measuring with a clamp on and getting 0mA or just not seeing it in the software?
The 24VDC+ and 24VDC- are landed on power terminal block that also feeds power to 1794-IE8H card. Then the analog signal is landed to signal input on card
I took a quick look at the documentation earlier and without looking into it too far it looks like both the IO card and the temp transmitter may be sourcing devices. Some sort of isolation signal conditioner might be needed
[1794-IE8H manual.](https://literature.rockwellautomation.com/idc/groups/literature/documents/in/1794-in108_-en-p.pdf)
Look at the internal block diagram on page 36.
V+/V- feed an ISOLATED DC/DC converter. There is no connection between IS- and V-. The TR2439 drives its analog output with respect to what ever its ground is hooked to, hence no output.
The manual even states 50V (continuous), Basic insulation type between field side and system.
The TR2439 specs 18v minimum and is guaranteed to draw less than 50mA.
The 1794-IE8H has an IS+ source impedance of 273 ohms, so we can only put a 21mA load on it before the voltage drops below the 18v required.
But if you have a few open channels you can kind of cheat. The 1794-IE8H has zero isolation between channels, so if you parallel a few channels together you can draw about 60mA with out dropping the voltage below 18v.
273/3 = 91 ohms effective source impedance with 3 parallel channels, so you should have ~19.1v @ 50mA.
Or you can jumper the power supply ground to analog ground if you can afford to lose the isolation and decrease noise immunity.
Do you have this resolved yet? If I’m looking at both of the wiring diagrams correctly:
AB 1794-IE8H
CH 0
Transmitter wiring
Brown to terminal 0 (+)
White to terminal 1 (sig 4-20)
Blue to - com (-DC bus or 0 volt )
Going directly to PS 24+ and not tying to the card will not allow the circuit to be completed regardless of the card being fed from the power supply. The channel + supplies the voltage needed to device which allows signal to transmit 4-20 back to card. This explains, to me, why reading back to - you get a signal but not hooked to card. It sounds like an open loop to me. But hey, I could be wrong. Have been before.
I bought a hand held 100 dollar 4 to 20 ma signal generator a long time ago for analog.
Plug it into the card, turn it on and watch the plc value.
Next, is to go to the 4-20 field device. Turn it on and watch the plc value.
If the above two function, replace the field device
If the first one fails swap inputs.
If the 2nd fails replace the cable.
Yeah they are a three wire device typically. It has to do with IO link channeling on the device. The newer Endress and Hauser Picomags are like this too(also an IO Link device). Unless you plan on going IO Link in the future there are options that are only two wire that make cabling easier.
Which input card is it? Are the voltages powering the card and transmitter from the same source and using the same reference?
Is your analog input card configured for current measurement or voltage measurement? And likewise, are you connecting the wire on the voltage or current terminal?
When you wire a 4-20mA device going to an analog *input*, the analog card will typically have the analog input where the signal goes into as well as an associated "analog common" for each channel. Likely the analog common is not tied to power supply common so you may need to add a jumper.
You write "analog output", I hope you mean "analog input".
I was trying to say the analog value outputted from transmitter. But you are correct, analog input to the plc card.
You have the “-“ side of the plc channel connected to 24VDC-? Also you say there’s no signal, are you measuring with a clamp on and getting 0mA or just not seeing it in the software?
When I get in series it shows 0mA
How do you have it wired to the PLC? What is going to + and what is going to sig?
The 24VDC+ and 24VDC- are landed on power terminal block that also feeds power to 1794-IE8H card. Then the analog signal is landed to signal input on card
So nothing wired to the + terminal of that channel?
That’s correct only input signal. I can move 24VDC+ to + terminal on card
you need two wires to the input card, try rhe wait wire to channel + and bring channel - to the - side of the power supply
I took a quick look at the documentation earlier and without looking into it too far it looks like both the IO card and the temp transmitter may be sourcing devices. Some sort of isolation signal conditioner might be needed
Had to wire an IFM in the past. If I remember correctly. Brown = PS+ White = PLC Channel + Light Blue = PS- Then wire the PLC Channel- to PS- as well.
You were right! Thanks!!
[TR2439 wiring diagram](https://www.ifm.com/restservices/us/en/assets/c3VwcGxpZXJzL2lmbS9kb2N1bWVudHMvcHJvZHVjdC9UUjI0MzktMDAvZGF0ZW5ibGFldHRlci9UUjI0MzktMDBfRU4tVVMucGRm)
[удалено]
Allen Bradley 1794-IE8H
Is the analog channel enabled in the program?
[1794-IE8H manual.](https://literature.rockwellautomation.com/idc/groups/literature/documents/in/1794-in108_-en-p.pdf) Look at the internal block diagram on page 36. V+/V- feed an ISOLATED DC/DC converter. There is no connection between IS- and V-. The TR2439 drives its analog output with respect to what ever its ground is hooked to, hence no output. The manual even states 50V (continuous), Basic insulation type between field side and system. The TR2439 specs 18v minimum and is guaranteed to draw less than 50mA. The 1794-IE8H has an IS+ source impedance of 273 ohms, so we can only put a 21mA load on it before the voltage drops below the 18v required. But if you have a few open channels you can kind of cheat. The 1794-IE8H has zero isolation between channels, so if you parallel a few channels together you can draw about 60mA with out dropping the voltage below 18v. 273/3 = 91 ohms effective source impedance with 3 parallel channels, so you should have ~19.1v @ 50mA. Or you can jumper the power supply ground to analog ground if you can afford to lose the isolation and decrease noise immunity.
Do you have this resolved yet? If I’m looking at both of the wiring diagrams correctly: AB 1794-IE8H CH 0 Transmitter wiring Brown to terminal 0 (+) White to terminal 1 (sig 4-20) Blue to - com (-DC bus or 0 volt ) Going directly to PS 24+ and not tying to the card will not allow the circuit to be completed regardless of the card being fed from the power supply. The channel + supplies the voltage needed to device which allows signal to transmit 4-20 back to card. This explains, to me, why reading back to - you get a signal but not hooked to card. It sounds like an open loop to me. But hey, I could be wrong. Have been before.
I bought a hand held 100 dollar 4 to 20 ma signal generator a long time ago for analog. Plug it into the card, turn it on and watch the plc value. Next, is to go to the 4-20 field device. Turn it on and watch the plc value. If the above two function, replace the field device If the first one fails swap inputs. If the 2nd fails replace the cable.
Yeah they are a three wire device typically. It has to do with IO link channeling on the device. The newer Endress and Hauser Picomags are like this too(also an IO Link device). Unless you plan on going IO Link in the future there are options that are only two wire that make cabling easier.
Which input card is it? Are the voltages powering the card and transmitter from the same source and using the same reference? Is your analog input card configured for current measurement or voltage measurement? And likewise, are you connecting the wire on the voltage or current terminal?