1734-VHSC24 Pulse Flow Meter

[eight_bools]

Morning Guys,

I am installing a turbine flow meter with a pulse output to measure flow on a compactlogix 5069 -L306ER through a 1734-VHSC24. Never used a flow meter other than an analog output and never used a counter card. Does anyone have any sample logic they could share? I am trying to capture instantaneous flow and total flow over a period of time. I’m sure I can figure it out but it’s always helpful to see it working to get started.

If all goes well I have another flow meter and counter application I would like to convert to hmi control through a plc filling bags and utilizing the outputs on the counter card.

Any input is appreciated.

 

[Ken Roach]

The POINT platform has two different categories of high-speed counter cards.

The 1734-VHSC5 and -VHSC24 are most similar to the "HSC" functionality of their modular predecessors in the PLC-5 and SLC-500 platforms. They are built to count fast pulses and trigger onboard outputs very quickly based on a threshold or window.

The 1734-IJ and -IK are "Encoder Input" modules. Why they didn't just call them -ENC5 and -ENC24, I don't know, but the input voltage is the only difference.

Those modules don't have onboard outputs or threshold/window comparators. Instead they deliver over the POINTBus and network a value that is based on simple pulse counts, quadrature up-and-down counts, or a rate value.

So if you're going to choose POINT modules for various applications, take careful look at both VHSCx and IJ/IK. The VHSC also ships with an unlabeled second module that gives you the option of providing encoder power supply terminals.

The good news is that 1734-VHSC feature set includes (afaik) all the same features for rate measurement as the IJ/IK, and more. Check out the Rate Measurement section of the 1734-UM003 User Manual for details on how to set that up.

Your second question is basically "how do I create a flow totalizer in Logix 5000".

The POINT modules don't have a totalizer built in (there's a 1756-CFM flowmeter module that does), but there is a TOT instruction that is available in the Logix Structured Text and Function Block Diagram languages.

It is documented in the online help, and in the 1756-RM006 Process Control Instruction Set Reference manual.

 

[eight_bools]

Looking at the manual I think I am going to use counter mode to count the number of pulses and divide by the k-factor of the flow meter to get liters.

So I will be using input A to increment the count and input B will be left floating to count up. I am wondering though if I connect the output of my flow meter to A and the ground/common to Aret. The manual does not really explain what Aret is used for so I am just guessing. Does anyone have any experience with these modules that can confirm what Aret is used for. This is the manual that I am referencing.

I also attached a photo of the wiring for the module and my flow meter.

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1734-um003_-en-p.pdf

 

[drbitboy]

Links from @Ken Roach to more documentation are here: https://www.plctalk.net/qanda/showthread.php?p=927907#post927907

The installation manual link is here: https://literature.rockwellautomation.com/idc/groups/literature/documents/in/1734-in003_-en-e.pdf, but it covers the A/B/Zret terminals with no more detail than the User Manual.

The manuals never explicitly state what the Aret/Bret/Zret terminals are, but the Q-article @Ken references states they are connected to Common (Ground), which seems to me to not exactly, or at least rather indirectly, answer the question "What is the purpose ...," but I guess it's close enough.