1769-IQ16F Card for Speed Measurement

Hi All,
I am using CompactLogix L33ER with a 1769-IQ16F card for a rotating machine shaft ( drive and driven pulley arrangement with V belts ) speed measurement. There is a Turck Inductive sensor in the field capable of 1Khz switching frequency. The shaft actual speed is 485 rpm but the counter in studio5000 is readying 402 pulses in every minute.
As part of troubleshooting, I changed the striker/target size and every time I got different number of pulses. Size x of striker gave 96 rpm, size 4x gave 250 rpm and size 10x gave 402 rpm.
I changed the filter On to Off and Off to On to 0.1 msec but same result. RPI for the card is set at 20 msec which I am not sure if it is correct.
Main Task is set to Continuous Type with 500 msec watchdog time value set.

In summary, card is not able to capture every pulse. Any tips, suggestions to fix this problem would be highly appriciated.

Thanks

That appears to work out to 123msec per pulse, so unless your striker is tiny you should be able to pick up a reading.

Obvious answer is encoder/tacho but may be cost prohibitive.

Assuming this isn't VFD controlled so you can't just pick up the speed from there?

If you look at the Monitor tab of the Task Properties, what is the Scan and Interval Times.

Create a separate periodic task that simply deals with that input and change the tasks priority setting to 1.

Puddle said:

That appears to work out to 123msec per pulse, so unless your striker is tiny you should be able to pick up a reading.

Obvious answer is encoder/tacho but may be cost prohibitive.

Assuming this isn't VFD controlled so you can't just pick up the speed from there?

Click to expand...

No, its a Direct Online starter application.

jstolaruk said:

If you look at the Monitor tab of the Task Properties, what is the Scan and Interval Times.

Create a separate periodic task that simply deals with that input and change the tasks priority setting to 1.

Click to expand...

Thanks for your response.
I have made changes as you have advised.

Currently I do not have access to the system running at the site so can not see the actual scan and interval times. However, I will test these changes once I have access.

Thanks

Welcome to the PLCTalk forum community !

Unfortunately the Compact I/O bus and any discrete module connected to a proximity sensor is not a great way to measure the speed of a pulse signal. The modules don't have onboard counters, and the 1769 Compact I/O bus doesn't have fast interrupts.

The 1769-IQ16F is definitely faster than other modules of its class; the ordinary 1769-IQ16 has a fixed filter of 8 ms off-to-on and on-to-off that is intended to make it resistant to 60 Hz interference.

But it can't get data into the PLC program any faster than the ordinary Requested Packet Interval (RPI) rate for the module.

If you can approach this application by counting the number of microseconds (use a GSV instruction to grab the CST timestamp at the start and stop of an accumulated count) for a relatively large number of pulses, with the RPI turned down as far as you can, you are likely to get the most accurate results.

Ehsan-ul haq said:

Thanks for your response.
I have made changes as you have advised.

Currently I do not have access to the system running at the site so can not see the actual scan and interval times. However, I will test these changes once I have access.

Thanks

Click to expand...

Hi all,
Just an update to close the topic for everyone's benefit.
I made below changes and it worked perfectly.
1- Created a separate Periodic Task
2- Changed period to 0.5 msec ( Just enough to avoid task overlap count)
3- Gave priority 1
4- Changed RPI of the IQ16F to minimum value of 0.5 msec
5- Configuration of data Filter (Off to On and On to Off 0.1 msec)


Thanks for everyone's help.

Thank you very much for the followup and feedback !