1734-vhsc24

Hi I am looking at a new project where i will probably select a 1734-VHSC

I need to collect flowmeter pulses from 2 flowmeters at a maximum rate of 10 litres per second (10Hz)

I need to determine the litres/min instantaneous flow rate for each

I also need to determine the difference in Litres between the flowmeters if a valve is opened (flow2-flow1=whats gone out the valve)

I have not dived into the manual yet but can I assume the 1734-VHSC is the correct part for this task and is their any pitfals i need to consider

The PLC will be a L18ER tpye

Thanks

What is the pulse rate of the meters? What type of pulse transmitters are on the meters?

The reason why I ask is you may be able to get away with using the onboard inputs for your pulse counting. The L18 manual doesn't give a max input frequency for the DIs but shows a off to on min time of .5 ms. So in theory the input could handle a 800HZ signal. I am assuming a pulse width of 0.6ms.

Might be worth looking into.

Hi the pulses are a square wave so eaual space and mark. The expected count is 10 per second.

The system is going to replace a Mitsubishi PLC which uses high spes ounters so this method is in the customer URS .

They have much confidence in high speed counters and I only have a short time to deliver a working solution.

I think I will get onto technical

Thanks for the opinion

There are two models for different input signal voltages; 1734-VHSC5 and 1734-VHSC24.

While the usual purpose of a HSC/VHSC in the Allen-Bradley world is to allow you to set outputs quickly based on an encoder count, the 1734-VHSC modules also have several Rate measurement modes.

My guess is that you want to use either Continuous/Rate mode or Rate Measurement mode. There are some differences on how they calculate the rate and update the internal registers, so read up in Chapter 1 of the 1734-UM003 user manual.

Even though the module has three input signals (A,B,Z) to handle quadrature encoders, it only has one counter subsystem. To monitor two flowmeters, you need two modules.

Hi Ken
It will be the 24V version.

Thanks for the tip about 2 counter modules my AB rep didn't tell me that

There are really four high-speed counter type modules for the POINT platform:

1734-IJ (5V signals)
1734-IK (24V signals)
1734-VHSC5
1734-VHSC24


The -VHSC modules have output comparison windows and physical outputs onboard.

The 1734-IK might be the more appropriate module for this application, since you're not running outputs directly from the module. It also has the Period/Rate and Rate Measurement modes, so it would be suitable for use with flowmeters.

Thanks Ken

Hi This project is now on my desk and i have set up the HSC as continuous/rate. I am receiving a count in Local:2:I.StoredData for each pulse but no rate value

I need to acheive an always running litres/min and also a 'count' from when a flag goes high (valve is open)..remember i have a flow meter each side of the valve

I have rolled my own rate value of pulses/min in a task running every second and subtracting the previous value from new value and populating a fifo of 60 counts and then adding it up

I can do the another roll my own for the valve open differential counts but it seems i am only using the HSC to collect pulses and not using any of the functionality

Is my application a bit out there or am i missing somthing

Thanks

1734_vhsc

I am interested in asking Rockwell if this is a case of "one or the other" re: the card's versatility.

On the subject of wiring and configuration, I couldn't follow the detail in the um003 and im003 manuals, (still not convinced that they are in there) but I am also on my 1st project using a shaft mounted encoder (A, NOT A, B, NOT B, Z..) with the point I/O module. I haven't been able to populate the "POINT_I/O:7:I.PresentData" dint. I can preset it and the LED's flash when the motor is turned. Also, I discovered that my encoder was transmitting a 5v signal even though it is sourced from a 24v power supply, so I spec'd the 1734-VHSC5...

As for configuration, this thread explained more for me than I could get out of documentation. Thanks for posting!

I will look into setting my configuration to "Continuous/Rate" to get my required count. Thanks, again.