The pictures are of a Dura Pulse drive. The speed reference is going into ACM & AI1 terminals on the drive, but first the wires are going through this homemade board. Any ideas on what this is doing and why??? Thanks!!!
At first I was thinking it's probably converting from a current reference signal to a voltage reference input, i.e. 4-20ma to 0-10VDC because AI1 is the 10VDC speed reference signal input. But that only really takes a resistor and this has at least 2 resistors plus a cap. Besides, if they wanted to use the 4-20ma all they had to do was terminate on AI2.
Well that's what a PI or PID loop is for, or even the accel/decel rate programming. But I suppose if someone didn't know that they could have tried to do it externally.My WAG is a low pass filter to reduce any fast changes in the input signal. It would keep the VFD from making any fast changes in output speed.
What's the input from, and what is is driving??
110527-1246 EDT
My guess is that red and black are a power source to the device at the end of the cable. This might be as simple as a potentiometer. It appears there are two 5.6 K resistors. and possibly a 25 to 100 mfd capacitor.
Seems pretty clear it is a filter or averaging circuit. Probably to reduce noise. If the input is a differential amplifier I can see a resistor in both input leads. But then it might be desirable to have a capacitor from each input to ground which I might expect is the black wire.
More needs to be known about what is at the end of the wire.
I am not familiar with the motor control and therefore what the various terminals are.
.
110527-1246 EDT
My guess is that red and black are a power source to the device at the end of the cable. This might be as simple as a potentiometer. It appears there are two 5.6 K resistors. and possibly a 25 to 100 mfd capacitor.
Seems pretty clear it is a filter or averaging circuit. Probably to reduce noise. If the input is a differential amplifier I can see a resistor in both input leads. But then it might be desirable to have a capacitor from each input to ground which I might expect is the black wire.
More needs to be known about what is at the end of the wire.
I am not familiar with the motor control and therefore what the various terminals are.
.
110527-1246 EDT
My guess is that red and black are a power source to the device at the end of the cable. This might be as simple as a potentiometer. It appears there are two 5.6 K resistors. and possibly a 25 to 100 mfd capacitor.
Seems pretty clear it is a filter or averaging circuit. Probably to reduce noise.
I agree. A filter. The electrolytic capacitor and relatively high value resistors suggest a DC signal. The implementation looks like an amateurish bodge to fix a field problem.
110527-1719 EDT
steve66:
It is really hard to tell with the photo resolution. I read the colors as green, blue, red, and silver. I sort of worked back from silver and red (now I think red is orange) and tried to visualize the spacer bands. I think an AB (Ohmite) would have been easier to read. Whatever the resistance it is only a bandwidth factor..
C3PO:
So if AI1 is the speed command what is it referenced to? I suspect it is ACM. If so, then is ACM tied to the power system EGC?
At the DAC end I have to assume it is the voltage source and probably referenced to its own EGC. If this is the setup, then there are big ground noise problems..