ABB WaterMaster Wiring – Pulse Signal

[JoelAB]

I am new to this forum and coming here as a novice to PLC work and signal However, my questions here hopefully won’t pertain to PLC programming. I have been tasked with connecting telemetry equipment on to various water meters in a water system to provide data for regulatory reporting. For the most part the water meters are already wired to the SCADA system but data retrieval from that system is not possible due to security issues. I’ve resorted to using the pulse output to the telemetry equipment to pull the meter data. (For most of the meters the pulse output is un-utilized in the SCADA system) However, I’ve now come to two water meters which have the pulse output (and 4-20mA) being utilized by the SCADA PLC. These water meters are ABB WaterMaster Mag Meter and Transmitter. I’ve attached an image of the pulse signal wiring from the user’s manual. D01 is for forward flow and is being used, D02 is for reverse and is not utilized.

Q1: I’d like figure out a way to connect to the pulse signal in parallel at the water meter transmitter location. Is this even possible since the pulse signal is powered through the PLC?
Q2: It seems that it might only be possible if I could wire my device in parallel with the PLC load, and with an equal resistance. Is this correct?
Q3: Are there any other options I am not thinking of, that wouldn’t require connecting to the PLC or SCADA system? Security issues prevent me from doing this.
Q4: Lastly if anyone is familiar with ABB WaterMasters, is it possible to use DO2 for forward flow by reprogramming the transmitter?

Thank you

 

[Oceansoul]

What is the SCADA system, and what is the telemetry system? Which RTU onsite for the telemetry? Could you use a 4-20mA "splitter" to take the 4-20 output from the watermaster to both SCADA PLC and telemetry RTU?

 

[Saffa]

DO1 / DO2 unfortunately can only have specific functions (see page 22 of the programming manual, document name IM_WMP_G.pdf) so you can't configure both for forward pulse.

The outputs are also polarity sensitive so unless both PLC and RTU have sourcing outputs and run off the same voltage supply you won't be able to parallel them up. Even then... not sure it would work reliably.

One solution would be to use a solid state relay with two poles (or two single pole units in parallel) to isolate the two devices. Don't use standard relays.. you will only get a few years out of them if the pulse rate is high.

 

[JoelAB]

Oceansoul - the RTU is a Banner DXM. I have been considering using a 4-20mA splitter for other sites where 4-20 is the only option but my client has been un able to provide a decision on this. I expect the same indecision for this location. Likewise I am still trying to get the info on the SCADA system. The issue with pushing data from the PLC, like you'd expect, is the clients security concerns. Being able to intercept the signal from the meter without interference to the signal to the SCADA was the preferred option.

Saffa - Thank you for the relay suggestion. I will look into how I might implement this.

 

[JoelAB]

Saffa, I had a chance to review the PLC cabinet and pulse signal associated with the water meter. Here is the wiring of the signal.

+24V --> power distribution terminal block --> ABB Watermaster (COM)
ABB Watermaster (DO1) --> signal terminal block --> PLC DC Input Module --> -24V

It seems reasonable that DO1 would be wired to the SSR input (+), and SSR input (-) to the DC Input Module. Or does an SSR input need to be connected to ground? Hence your recommendation for the the two pole SSR.

 

[Saffa]

SSR negative to 0V would be how I would do it. Then move the existing PLC input and 24V+ to one pole of the SSR. Use second pole for your gear.