Wednesday, July 21, 2010

A Lot Less Blood, Sweat, and Tears for the Spinning Wheel

OK, I really stretched on the title of today’s post, but I feel like I’ve got some added pressure because of Jim Cahill’s blog yesterday on Emerson Process Experts. Yesterday I told you about the new capabilities built right into the DO CHARM in version 11.3 of DeltaV and its electronic marshalling. Today I’ll share some of the features associated with the DI CHARM.

So first, the DI CHARM can be configured as a pulse count input channel. Now the top frequency is only 10 kHz compared to the 50 kHz of the existing Multifunction IO card, whoever bought a Multifunction IO card? No, really – in the last 10 years, I can count the number of Multifunction cards we’ve used on projects on one hand (and have fingers left over). And the 10 kHz of the CHARM is WAY higher than configuring a channel of a standard DI as a pulse input, which has a frequency limit of a paltry 75 Hz.

Like the Multifunction card, not only do you get access to a counter (going up to 65535), but you get a FREQUENCY value, very handy for determining speed – you don’t need to worry about some 3rd party pulse to 4-20ma converter to figure out how fast you’re spinning.

For testing, we wired a DO CHARM configured as a Pulse Output (see yesterdays post) into a pulse count DI CHARM. The PULSE_PERIOD on the DO CHARM was set to 0.02 or 20 ms. The picture below is from the module I have running at 1 second:

The FREQUENCY value coming from the DI CHARM is 50 Hz (I love it when a plan comes together). FYI – the setpoint of the AO can be used to adjust the pulse width coming out of the DO CHARM. With a setpoint of 30%, the actual pulse width would be 4 ms.

I touched on some of the new signal characterization features for DI CHARMS back in March, before I actually had CHARM hardware to play with. One of the first things I tried out when I got my CIOC and CHARMs was the Extend Output Filter. How many times have you had to develop logic that monitors for an operator to press a button in the field? You stress about “what if he doesn’t hold the button long enough?” or “how fast am I going to have to run my module to pick it up?” With the Extend Output Filter, you can configure how long it would hold the “1” from the momentary button press at the CHARM. The dropdown lets you pick a filter time anywhere from 50 to 30000 ms. Selecting a time of 1100 ms would allow me to run my module at 1 second execution and feel comfortable in knowing I’ll not miss the quick tap of a button.

Output filter types of Latching PDE and Latching NDE are still in the dropdown list, but I’m not sure it’s really implemented in version 11.3 – stay tuned.

1 comment:

Jim Cahill said...

Bruce, Like a true professional you rose to the challenge! Great post!