Quote:
Originally Posted by Mike Copioli
Since the FRC control system has several voltages, 5v, 12v, 12v boost, 24v boost it is possible for only one device to brown out based on its location, wiring, and individual power requirements.
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The idea in this case would be to rig the comparator to have either various references, possibilities include:
1. A unity gain buffered non-forced voltage out D/A converter (most voltage out D/A converters are buffered somehow).
2. One of the various reference voltage components already available for various conversion systems (some of them can be 'in-system' calibrated).
3. A 'digital potentiometer' in a voltage divider configuration possibly with a unity gain buffer.
One can measure current using a shunt resistor, and I have dug out my collection of 2 milliOhm 30W shunts because using a inductive current probe is just a double problem. A standard Rogowski coil probe would be slow and limit your reaction time to about 3uS using most off the shelf components (and it assumes the hall effect sensor is capable of measuring DC saturation of the coil). So even if you did want to sample, you'd probably top out around 100,000 samples per second before you alias. Obviously a professionally designed oscilloscope current probe responds faster than this, but it's coil size is small and it's amplification circuits expensive and more difficult to calibrate. I can't see spending $400-$2,000 on this...possibly per device.
I was concerned about using the shunt in other posts because I wasn't convinced I could find a ready source of this wattage and value shunt resistors, but I found one. Lucky enough the stall current of each CIM isn't much higher. I just don't think telling people to trim their own shunts is going to work out unless they have a precision meter or bridge.
As to the placement, I figure the device has to be designed to be connected at the device that you think is 'browning' out. This includes the shunt resistor which should be on the load end.
In case it's not apparent where I'm going with this, as the concern here isn't purely passive circuit dynamics, I'm gearing up to create a way to check the phase relationship and magnitude of the voltage and current by setting the levels to where you consider anything beyond or below that a failure. Then latching that state. So the instant something slips out of the range of 'acceptable' you merely get an indicator that you have a problem. If you really wanted you could use a S/R flip flop on that configuration (like a 555 timer) and then use a digital device like a cheap PIC/AVR to do some QOS analysis. For example...how many times did you slip out of range....how long approximately was it out of range?