Dividing Relays

We have nine flow meters with pulse access modules. The SLC/505 with 1746-IV16 input module won't detect the pulses because they're too fast. I can detect the pulses if I throttle the flow, but that's not desireable.

I've been considering using dividing relays (Electromatic), but can't find a supplier who has enough. Also, it looks like they're discontinued (at least model SP239120).

Looking at the on-line manual for a Micrologix 1400, it appears that I can have up to 8 high speed input sources attached (4 for HSC:0 and 4 for HSC:1), or does this mean I can only have two?

Is anyone aware of a PLC or dividing module with 9 or more inputs / outputs?

what about a few of these?

1746-HSCE2⋆*
High-Speed
Counter Module 4 single-ended or 2 differential quadrature inputs (5, 12, or 24V DC) 1 MHz 4 outputs
(5V DC, 12V DC, or 24V DC source) 1.5 ms max. 1 250 mA @ 5V DC 1746-RT25G
Description — The high-speed counter module is used in control applications where the ability to detect high-speed machine or process motion is critical. It has 4 counters, but only 2 can be used with quadrature inputs. When configured for class-1 operation with any SLC processor, it provides 16-bit counters with 8 input words and 8 output words. When configured for class 4 operation, it provides 24-bit counters for count ranges of ±8,388, 607 with 23 input words and 8 output words. It has 4 source outputs so that the control loop is closed on the module without going through I/O or program scan delays. Typical applications include packaging, material handling, flow monitoring, cut-to-length, motor speed control, and machining.

Spectrum Controls (an AB partner) sells 8 channel pulse/meter cards, I love them, much easier to configure than the AB HSC cards.
http://www.spectrumcontrols.com/ab-1746.htm

The micrologix has only two high speed counters, or two four wire quadrature inputs using the first 8 inputs (for encoders). Its probably not what you are looking for.

Spectrum Controls has 1746sc-CTR4 and 1746sc-CTR8 flow meter modules for SLC500, that is probably your best bet short of changing to a different kind of flow meter.

(edit: Ken beat me to it.)

Can you not change the pulse width or frequency?

Do you need to be as accurate as each pulse is providing, are you acting on this accuracy? If you are looking at dividers, then I suspect you do not need the accuracy provided?

Most meters that we deal with can have the pulse rate or width configured.. Unless they are paddle type meters of course??

Thanks for the replies. Meters are turbine-type. I just ordered a 1746-CTR8. Should arrive my Monday.

A solution for future problems like this: Omega Engineering, Red Lion, and Acromag among others have signal conditioners that convert a high frequency pulse to 4-20 mA. I've used the Red Lion version with good success in the past.

Installed the 1746-CTR8 today. Had to install a DPDT relay in order to get the 9th meter connected (meters #8 and #9 are never equired at the same time).Had to 820 Ohm pull-up resistors on signal lines.

Note to anyone attempting this with turbine flow meters - make sure debris doesn't interfere with turbine movement. I found a small piece of PVC in the first meter I connected... after an hour of checking connections and module configuration words!

Thanks for suggesting the CTR8

Tom Jenkins said:

A solution for future problems like this: Omega Engineering, Red Lion, and Acromag among others have signal conditioners that convert a high frequency pulse to 4-20 mA. I've used the Red Lion version with good success in the past.

Click to expand...

Tom using the 4~20 do you loose any accuracy? I did a few jobs where I tried to totalize of a 4~20 signal and kept getting drift. Once I changed to pulses everything cleared up.

Any Frequency to current converter has to do some sort of averaging over time. If this is too long, you won't be seeing what is really going on. If it is too short, the output will likely oscilate.

Did the converter have the ability to change the averaging time?

You can lose accuracy if the calibration isn't right.

It depends on what you are trying to accomplish. If you want to totalize then pulses are better. If you are just monitoring a process for general information then it doesn't matter. If you are doing custody transfer, and $ are involved, then stick with pulses and buy the right number of high speed I/O to do it right.