S71200 HSC Slow to Respond to changes

[JesperMP]

Oh, by the way.
Most counter modules can be set to calculate the rate.
I know that the ET200S counter modules can do that. Dont know about S7-1200.
In that way you are relieved of any programming effort whatsoever.

 

[[email protected]]

Thanks for the reply jasper.

Wel I simply have a HSC configured to measure frequency. The HSC is located within the PLC, it is not an external module that you connect to the PLC. I have attached a screen shot of the actual configuration.

As can be seen the HSC is configured to count frequency.

I am on my rig at the moment and I am definately going to have a major problem in counting the number of paper pulses. When i change the frequency of the paper pulses from 15 papers/sec to 16 papes per sec, the display jumps from 25200 C.P.H to 28800

 

[JesperMP]

Cannot see any screenshot. Also do not have any experience with S7-1200.

I am guessing the module is set to update every 1 sec.
If you can, try to change the update rate to once every 10 seconds.

 

[[email protected]]

sorry here it is

 

[JesperMP]

In the bottom of the picture is a parameter "Frequency measuring period". Try to set it to 10 sec. The accuracy should increase by a factor 10. But then there will be 10 seconds between updates. Thats the trade-off.

 

[TurpoUrpo]

There is no option for 10 seconds. 0.01, 0.1 and 1 sec only.

 

[JesperMP]

I see. In that case I see no other way than switching over to the method I described before.

 

[tim2]

Thanks for the reply jasper.
When i change the frequency of the paper pulses from 15 papers/sec to 16 papes per sec, the display jumps from 25200 C.P.H to 28800

What else would you expect it to do? It added 3600 to it, which it should for an increase of 1 per second.

I guess maybe I'm not sure what you are doing. If you want the current "copies per hour" rate updated with what is passing every second, you will have the rate jumping around by 3600.

Can't you just use a counter, or the HSC if your pulses are too fast for a regular counter, set it up pulses for some amount of time, then base the value on that?

You also wrote "i need the accuracy to be within 50 or 60 copies per hour"

THere's no way counting pulses for a second an multiplying by 3600.

Not trying to be an ***, but why not configure the HSC to count for an hour and use that value? Or some sort of averaging routine that counts the pulses for a few minutes then multiply by a much smaller number to get the pulses per hour?

 

[VoltSmith]

BennyK,

You mentioned, you increased the rate from 15 papers/sec to 16 papers/sec. But 25200 C.P.H equals to 7 copies/sec, and 28800 equals to 8 copies/sec. Recheck your system.

Rahul

 

[[email protected]]

I am using a two pole motor that spins past an inductive sensor to simulate pulses. Sorry i mean when I applied 15Hz to the two pole motor i got 25200 CPH which is 7 papers per second.

Wel I guess the problem is that the HSC can only determine the speed from the actual physical pulses it can detect. I.e it can indicate when there is 7 pulses per sec and then 8 pulses per second etc but it can indicate when for example 15.4.....15.5.......15.6.....15.7.....pulses per sec etc are present. this is where I am falling down.

I take it that there is no way of configuring a HSC that counts pulses per second to determine an intermediate speed value such as 7.6 pulses per second?

Jasper seems to have a viable method (above), i must study it more. I am not sure how to implement it on an S7 1200 doe?

 

[[email protected]]

Hello everyone,

Just to let ye know I have completed the program and it seems to be working correctly. in order to solve the problem I have created a cyclic interrupt that moves a totalised count every 30 sec to a memory location. this interrupt also sets the CV of the HSC to zero. I can then calculate the speed by carrying out a floating point calculation and them converting back to a double word.

thanks to everyone for their suggestions

regards,
Brendan