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Thread: INTEGRAL TIME
01-29-2005, 05:17 PM #1
having recently been thrown under the bus by my service manager. "hey we are doing ddc now here is a laptop with lonspec do these jobs" and no formal training i have managed to learn to write some basic control loops. i have been hung up on how throttling range, integral time, derivative time, etc effects control loops are there any online sites or books that can help eliminate my constant banging my head against the wall.
01-29-2005, 06:54 PM #2
Honeywell has had their Gray Engineering Manual in publication for 30+ years and it still contains a lot of good information. It is available for download at the Honeywell website:
On the right hand side you will see Related Information, and then below that is the link to download the Manual. Right click and then do the "Save Target As" to save the file to your PC. Be aware, it is a large download (7 Mb) for dial-up.
Once you have the manual open the document pages 21-25 of the manual (pages 31-35 of the pdf) have an explanation of P, PI and PID control. Hope you find this helpful.
01-30-2005, 01:16 AM #3
hanknerd thanks for the info. ddc is based on pneumatic control fundamentals and the principals still apply. for a guy thats been humping pipe and compressors up ladders this seems to be an opportunity for me to save my body and extend my career. commercial service takes a toll on the body and at 42 yrs old and 15 years doing service work and
using a shovel for a living before that i see ddc as an way to save the knees and aching back. it seems you never have the time on jobs to fully understand the principles of what your doing with the nextel and pager running your rear off.
01-30-2005, 01:26 PM #4Professional Member
- Join Date
- Nov 2004
Also if you are configuring HW xl10's use the help button when in the PID loop tab, some settings are not what they seem on these devices. There is also an engineering document for each xl10 it is a pdf, search the document for PID and you will find in some cases a chart for the settings for different applications.
01-30-2005, 09:10 PM #5
Vice: Throttling Range and Integral are very important. I've seen all kinds of things. TR is the distance your input can vary to change the output from 0 to 100. For a room you want to use about 2-3 degrees, OA dampers use ~20. Let's use OA dampers as an example. Let's say you want to maintain mixed air between 53 and 57. If you enter a setpoint of 55 + or - 2 (4 TR) the dampers will continually overshoot and try correcting because it's too touchy. They will end up going full open which is too cold and then they will go full closed. By widening the TR you slow down the action. Now your setpoint is still 55 but you've got + or - 10 degrees or from 45 to 65 for 0-100% output. Now your problem is that it will settle out somewhere off setpoint like 47 or 58. By adding Integral it will keep "bumping" it closer to setpoint until it reaches it. I had a VFD that kept surging with a setpoint at 2" until I had the TR at 5"! We had a building with one zone valve on an entire wall. THey mistakenly put in a diverting valve and we ended up with a 60 degree TR. It just runs off the gain. Gain corrects a large TR. We never use deritive. You would have to watch it for a LONG time.
Itegral and Derivitive are from calculus. Integral is the area under the curve of how far off setpoint for how long. Derivitive is how fast is it approaching the setpoint (line slope).