A-B Micro800 High Speed Counter

Newbie here, in only my 6th month in PLC's. No previous experience whatsoever. I have been working with ControlLogix, now I have a job using Connected Components Workbench with a Micro820 controller. I need to configure a HSC to monitor a thru-put quantity and send an output signal to a remote multi-function control valve that controls a backwash/rinse of a water softener. I also need the HSC to act as a system totalizer. My problem is finding any literature/instruction, or video, on configuring the HSC. The only thing I have come up with is Allen-Bradley Article #688930 from the A-B Knowledgebase. Frankly, I'm just not able to wrap my mind around this with the A-B article. Any help is greatly appreciated.

Another note: the HSC will read a pulse generated by a "Hall Effect" flow meter. Having experience with 4-20mA sensors only, I can find no instructions to show the physical wiring of the flow meter to the HSC. I DO NOT have the meter present. It is installed in the field and my panel will be pre-wired to accept the field wiring at a terminal block in the panel. I presume the meter will be a three wire connector but unsure how it is to be wired in. Thanks again.

I have never used the HSC in the Micro line of PLC's but I can help you with the Flow Meter connections:
Normally a Hall Effect Sensor will have 3 wires.
Power + (normally 12-30Vdc)
Signal
Ground

So you will need to provide power from a DC Power Supply. You will connect the signal to the HSC + and the HSC Gnd to the Power Supply Ground.

Next you will need to find out the Meter's K-Factor. That is the number of pulses per unit volume. So it will be expressed as XXX pulses per gallon or liter or ??

Normally you would set the Preset of the HSC to the K-Factor (say 100 for this example). So every time the HSC counts to 100 it will set some kind of Done Bit. You can use that Done Bit to count Gallons or Liters or any units you want.

Hope this helps get you going.

Thanks Bullzi, that does help a lot. I do know that this particular meter, for this particular application (pipe size) has a K-factor of 7; pulses per gallon. I did find some more literature on the counter and appears that this counter is capable of a lot more than what I need it to do. Now, I just have to sort out what needs to be configured and what doesn't, and how to do it. Thanks again.

7PPG is a small K-Factor. You must have a pretty big line size. What kind of meter are you using? What kind of flow rates are you looking at?

All the HSC's do way more than I normally use. I looked briefly at the KB Article that you mentioned. You will mostly be concerned with the HPSetting on the HSC. Also set the HSCMode to 0 for a count up counter. That is assuming that you have flow in one direction only. When the counter is done you will be looking for the HSCSTS.Mode1Done bit to be true so you can count gallons.

Thanks Bullzi. The Instruction Block (IB) mentioned in the A-B article 688930 is an instruction block used in a Micro850 controller. I was instructed, by someone else, to simply import that IB from the 850 IB Selector. A bit more digging around led me to article 593048 with instructions to download and import the RA_HSCPlugin sample code. This instruction is also in the Micro800 Plug-in Modules User Manual, 2080-um004_-en-e.pdf. So, I now have the "correct?" IB installed and it IS different than the previous IB.

Meter is a Water King PW300 Hall-Effect paddlewheel with 3" pipe size.

244 gpm continuous flow with 324 peak flow. 7 pulses = 1gpm.

Following is the basic scope of the program:
An operator thru-put value is entered into HMI screen. Two softener bottles are available to go on-line. PLC designates one bottle on-line and begins counting gallons. At prescribed thru-put value, PLC sends 24vdc signal to bottle in "stand-by" to go on-line and resets counter. PLC then sends 24vdc signal to exhausted bottle to initiate regeneration. After execution of regen, that bottle enters "stand-by" mode until on-line bottle becomes exhausted (thru-put value is counted), at which point the process repeats. Each time a thru-put value is achieved, a signal is sent to the stand-by bottle, the counter is reset then a signal (delayed, another variable entered at HMI screen) is sent to exhausted bottle to begin regeneration. The regen process is controlled completely by a multi-function valve, on each bottle. A return signal is sent to PLC, from each MF valve, to confirm the valve is actually entering regen mode. Alarm will set if no confirmation signal is received.

One caveat...I also need to incorporate a "totalizer" into this program so that a total # of gallons is recorded and stored/displayed at HMI. I know this is a simple execution for most, but like I said in the original post, I am a beginner. I have worked with the mechanicals and process for years but have just recently progressed into the controls dept. There is not much opportunity for formal training. Thanks again.

With the flow rate and K-Factor you have you may be able to just use a standard DC input for your flow pulses. You are only looking at 38 Pulses per Second (Hz). That is about 13 ms per pulse. I couldn't find a max input frequency on the 820 but I think it may work.

As for the totalizer that is a pretty easy one. If you just want to count whole gallons then every 7 pulses you would add 1 to a DINT register. You can use the ADD block to add 1 to the total and then store that value in the total. See the attached.

Thanks Bullzi.

Bullzi, do you mind sharing the formula, or equation, used to calculate the length of pulse. Just to add to my reference library. Thanks.

Sure thing,
(Max Flow Rate * K-Factor) / 60 = Frequency at Max Flow
So for you: 325 * 7 = 2275 / 60 = 37.9 Hz

Now that you have the frequency you need to find the pulse width.
(1000ms / Max Freq.) = Pulse Period / 2 = Pulse Width (since the pulses are 50/50)
So in your case 1000/38 = 26.3 /2 = 13.15 ms

So your pulse will be on for 13ms then off for 13ms. If you know the the ON/OFF time of the input you can decide if the input will work for you. Most DC inputs I have seen in the PLC world are < 2ms ON/OFF but sometimes you can add some filtering to make the hysteresis longer via the PLC software. It really just depends on the hardware.

One other thing to keep in mind about using a standard DC input and counter in counting pulses is the PLC Program Scan Time. If the Scan Time is long because of a large or complex program it is possible to have the input go high and then back to low before the PLC can detect that the input changed state. I doubt that you will have this issue because 13ms is a very long scan time but it is something that you have to keep in mind. A HSC has its own processor that counts the state changes of the input independent of the PLC scan time. So it is not affected by the PLC scan time.

Most of the meters I work with in the Oil industry have a K-Factor in the 50 to 200 PPG and flow rates in the 600 GPM so if you do that math you will see that the Pulse Width is around 1ms and normally outside of the Inputs ability to detect a pulse. In that case a HSC is the only way to go.

Hope this helps you out.

Helps a lot, thanks again!