Anyone here have experience with multi-channel tachometers? I'm using a Deuta Werke type DF9 tachs with 4 channel output. These are typically used in heavy duty vehicles and things like commuter trains.
The problem is that I don't get any output from the 4th channel, and this is being seen as a pattern throughout our entire fleet. The outputs are open collector type. The tach datasheet says to use the formula:
Vout = ( (15 * Rload) / (1500 + Rload)), and cautions that Iout needs to be 10 mA max.
All I get when I setup channel 4 is a 24VDC signal with some noise on it. Rotating the tach has no effect on its output.
Are there any special tests I could perform to check the integrity of the channel 4? I'm worried that maybe channel 4 was never internally hooked up in the large batch of these tachs that we own. Is it possible that unused outputs of tachs can be damaged if left floating for a long time? Is there any local distributor or rep for Deuta Werke?
Thanks for the help.