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BillA · 03-02-2003, 12:02 AM

boy, we're sailing off the deep end here into testing, but I'm game (and obviously interested)

I think I have resolved the software 'issue', lets bank that one for a while

the control feedback/automation is of interest and potential utility
3 parameters being able to benefit: coolant temp, coolant flow, and air flow

the coolant temp is stable (±0.02°C fluctuation), but subject to drift as the outside temp changes form night to day
- the pump, chiller, and cross-flow brazed plate heat exchanger in the chiller bath are all outside
(too much heat and noise)
I suspect that with a DAQ board having a 16 bit analog output it would be simple enough to gin up an interactive chiller control
- the chiller is now remotely controlled with a precision microvolt (calibration) source, but such devices with GPIB control are VERY expensive (0.0001 VDC = 0.01°C)

coolant flow is a can of worms as the system length is ~11' and I have 3 oscillations of different periods
the flow rate is quite stable but understanding the actual range (to 'set' the mean can be vexing)
- I know of no single throttling (needle) valve whose effective range spans my flow rates (0.3 to 4 or 5 gpm),
nor with the sensitivity needed in an 'automated' controller
??
BTW, it does need to be set accurately for the 10 mountings as these are single point readings,
otherwise no, not at all critical - so long as accurately known

air flow can be difficult to stabilize, at specific flow rates the fans may sync, the flow start pulsating, really bizarre
(the compressibility of air is quite apparent)
I started with mechanical dampners, went to huge pots from welding machines (10A of fan current is no joke), to 115VAC fans with Variacs
- don't think its worth the effort (not actually running enough hours, at least for now)

I have a different question for you:
in running 4 - 20mA transmitters, I have a huge settling time (as in hours) to read at the 100pA level (Setra units, Foxboro only to 1µA)
which I believe is caused by the transmitters and not the meter, a Keithley 195A
-> can I switch in and out a resistive dummy load in the transmitter current loop when its not being read ?

03-02-2003, 12:02 AM	#24
BillA CoolingWorks Tech Guy Formerly "Unregistered" Join Date: Dec 2000 Location: Posts: 2,371.493,106 Posts: 4,440	boy, we're sailing off the deep end here into testing, but I'm game (and obviously interested) I think I have resolved the software 'issue', lets bank that one for a while the control feedback/automation is of interest and potential utility 3 parameters being able to benefit: coolant temp, coolant flow, and air flow the coolant temp is stable (±0.02°C fluctuation), but subject to drift as the outside temp changes form night to day - the pump, chiller, and cross-flow brazed plate heat exchanger in the chiller bath are all outside (too much heat and noise) I suspect that with a DAQ board having a 16 bit analog output it would be simple enough to gin up an interactive chiller control - the chiller is now remotely controlled with a precision microvolt (calibration) source, but such devices with GPIB control are VERY expensive (0.0001 VDC = 0.01°C) coolant flow is a can of worms as the system length is ~11' and I have 3 oscillations of different periods the flow rate is quite stable but understanding the actual range (to 'set' the mean can be vexing) - I know of no single throttling (needle) valve whose effective range spans my flow rates (0.3 to 4 or 5 gpm), nor with the sensitivity needed in an 'automated' controller ?? BTW, it does need to be set accurately for the 10 mountings as these are single point readings, otherwise no, not at all critical - so long as accurately known air flow can be difficult to stabilize, at specific flow rates the fans may sync, the flow start pulsating, really bizarre (the compressibility of air is quite apparent) I started with mechanical dampners, went to huge pots from welding machines (10A of fan current is no joke), to 115VAC fans with Variacs - don't think its worth the effort (not actually running enough hours, at least for now) I have a different question for you: in running 4 - 20mA transmitters, I have a huge settling time (as in hours) to read at the 100pA level (Setra units, Foxboro only to 1µA) which I believe is caused by the transmitters and not the meter, a Keithley 195A -> can I switch in and out a resistive dummy load in the transmitter current loop when its not being read ?