Created Date: May 12,2015

Created by: Dean

According to the meter manual all analogue outputs are self powered. Is that what you are referring to? Here is the relevant section from the meter manual.

Analog outputs are self-powered and have a

maximum load capacity of 500 ohms.

CAUTION: Do not connect analog outputs to circuits

supplying power. They are already powered.

For further clarification, see attached excerpt from the Do-More H2 manual regarding the F2-08AD-1

EDIT* Voltage across one of the analogue outputs on the meter measured at 15+ VDC.

Created Date: May 13,2015

Created by: Tinker

Your drawing looks ok at first glance, assuming the 1762-IF4 inputs are isolated from each other, while it is implied that that is the case I don't see it explicitly stated. A possible problem (but probably just a technicality) is that "maximum load capacity of 500 ohms ", the 1762-IF4 has an impedance of 275 and the F2-08AD-1 250 for a series total of 525, 525> 500, but not by a whole lot.

"Voltage across one of the analogue outputs on the meter measured at 15+ VDC. " 15 volts could push about 28mA through 525 ohms, so it would seem 20 should be manageable.

While the outputs of your transmitter are "self powered ", how it the transmitter (meter) itself powered? the F2-08AD-1 normally needs to have a connection to the 24VDC supply for the transmitters. If there isn't one, I imagine a separate 24VDC supply that shares the same common as the meter would do, but a 24VDC supply will need to be provided from somewhere.

If that 525 ohms did prove to be a problem (or if the 1762-IF4 channels are not isolated), another possibility would be to connect the "meter " directly to the F2-08AD-1 (providing the 24VDC from somewhere) and switch the 1762-IF4 to voltage mode and measure the voltage across the "Input Impedance 250?±0.1%, " of the F2-08AD-1, said voltage will be between 1 and 5V for 4-20mA. This is less than 1/4 of the -10 to 10V range of the 1762-IF4 so you'd be giving up a couple bits of resolution and would have to change the scaling in the AB code. So it is probably not an ideal solution, but it is an option if needed.

Created Date: May 20,2015

Created by: MikeMc

Mixed AB and ADC analogs

Dean you are not going to be able to do this unless you use a fully isolated AB IF4 module. The common connections in the ADC and AB guarantee that you are going to take the 4-20 ma signal to ground in two different places. Have you considered the easy way? Hook the 4-20 ma signals to the ADC chassis or vise versa and then on the other PLC use a DC analog input module wired across the 4-20 ma input on the other card.

Example if the 4-20 ma input card uses a 250 ohm load resistor for the loop the connection from +MA in and common will be 1-5 VDC. On the IF4 I seem to remember that in the module configuration you can select ma or dc mode so to see the same signal on two different PLC systems just monitor the DC voltage developed across the MA loop load resistor and scale as needed.

Also the only reason you got by with looping the 4-20 ma loop through multiple devices is that none had a ground on the loop before it got back to the power source. Even using an ungrounded power source won't help if there are 2 devices with the negative side of the loop grounded (as in VFD units).

Created Date: May 12,2015

Created by: Dean

I hope someone can help me clear my mind, because I think I have confused myself a bit. I have at present a process meter that outputs self powered 4-20mA signals associated with attached field sensors. There are 5 of them. Each pair of outputs shares a negative terminal on the meter. They are wired into a pair of Allen Bradley 1762-IF4 modules. What I want to do is daisy chain these into an AD F2-08AD-1. I thought I had this all figured out, but the more I look at it the more doubt I have. I have wired 4-20mA loops into multiple receivers before without any ill effects. I know the best method would be to use a bunch of isolator/splitters, but as you can see, I have 5 signals to deal with, and the budget just isn't going to withstand another $1000 requisition. The few times I have daisy chained an analogue signal everybody had their nice neat negatives and positives, and things went swimmingly. If you have the time, please take a look at the two attached pdf files. One shows the present configuration, and the second shows how I think adding the second input module should be done. Any help, guidance, warnings, or ridicule is encouraged and probably appreciated.