High Speed Counter NewDataFlag

Hi,

I am trying to write code for flow meter control. What I need to do is turn off the output for a valve if it is calling for product, but the flow meter is not counting pulses due to a fault condition (hardwiring the meter's fault output is the last solution). I have read the 1756-HSC manual cover to cover and found the NewDataFlag bit, which seems like it should do exactly what I need, but I am unable to get it to change states. I have enabled the StorageValue & wrote logic moving PresentValue to it to see if that was where the NewDataFlag was triggered. My eyes are now crossed & am in need of a sedative :-}

Any help would be greatly appreciated

I think you need to use one of the gate functions to get this bit to change state. It would then be set to '1' if the hardware gate condition goes true. I believe you then need to handshake it off.


Keith

Thanks... I guess I'll have to go back to the MOV & EQU ladder method. I was just wanting to continuously check that flow was present. Seems like there would be an easer way


Thanks Again,
Deb

The 'NewDataFlag' is triggerred (one for each channel) anytime, well, new data is available. That is, anytime the counter/rate (depending on mode) value changes.

Why this was implemented, I'm not entirely certain; perhaps it could be used to not bother processing counter logic unless there is something new to process, but with the speed of CLX, I've never bothered with it.

I doubt it would do much for your application, as it will be set no matter what new data is present. That is, you could receive one count, and have it set, or receive 1000 counts and have it set.

To check for continuous flow, I'd probably just read the counter in a periodic task (say, 100msec), and calculate the delta value between the last task scan, and the current one. Use the delta for a 'Flow OK' or 'Flow Bad" status.

According to the 1756-HSC manual, P 5-14, "I.NewDataFlag.0 Displays whether channel 0 received new data on the last scan. 0 = no new data was received, 1 = new data was received". Unfortunatly, while watching this tag online, the value never changed from 0. The manual says very little about this tag or how to use it.

Keith was probably right about it using a gate to initiate it