I'm trying to determine whether a typical Discrete Input Card (VE4001S2T2B1) will be sufficient or whether I should purchase a Multi-Function Pulse (VE4015) to read in the pulses from a turbine flowmeter. The pulse widths are 0.260 seconds long and will have a period of 1.5 seconds at maximum flowing conditions (0.66Hz). The system is an M-Series DeltaV. Has anyone had experience with something like this?
Thanks,Mike
These are very slow pulse rates. The standard DI is rated for I beleive 75 HZ. You're application indicates about 4Hz max, so yes, the typical discrete DI will work. There is a bit of a difference between the DI channel and the PCI channel on the multi-function card. The DI has a pulse count register that counts and cannot be reset. You have to handle the register in the control module. The PCI input is designed to use with the PIN block and offers a reset on the counter, as well as a configured flow rate based on the calibration of the pulses.
But you can definitly get the pulse rate of 4Hz handled with the typical DI channel.
Andre Dicaire
In reply to Andre Dicaire:
Any idea what the scan rate of the DI card is opposed to the Multi-Function card? It seems as though documentation on this system is hard to find. I do have the latitude to make the pulse duration, currently 0.260 seconds, shorter or longer when specifying the flowmeter.
In reply to Mike Hymel:
The Pulse count is generated at the card on a channel by channel basis. The card is scanned by the IO subsystem anywhere from 15ms to 50 ms, depending on the number and type of IO cards on that controller. When scanned, the card provides the pulse count register rather than a discrete state of on/off. The control module likely runs at 1 second, using the most current count.
The DI card provides 75 Hz resolution, so a period of 0.013 seconds. This can be either square wave or signwave so the puls duration should be about half this as a minimum.
The Multi function PCI is 50KHz, so a period of 20 microseconds, or a pulse width of 10 microseconds.
The standard CHARM DI's available in v11.3 DeltaV provide a 10 KHz PCI option, just to complete the picture.
Pulse counts need to be a minimum width, and have a maximum rate, typically the minimum width is half the period at maximum rate. So if the max frequency is 10 KHz, the perid is 10 microseconds, so the minimum pulse is 5 microseconds.
For the DI, the minimum pulse width is 0.07 seconds. max frequency 75 Hz.
Process Control TechnicianIntrepid Potash