NPN Open Collector
NPN Open Collector
(OP)
Hi, I have a Turbine oil flow meter installed and I need some assistance in relation to the pulse output signal. I am told that the meter provides a NPN Open Collector output pulse signal. There are three terminals on the meter (24V+,Pulse & Gnd). I have connected a 24VDC supply to 24V+ and Gnd. I would expect that the pulse signal would then be taken from Pulse and Gnd. However I am unable to determine if the meter is in fact working. Is there any way of checking (eg. using a multimeter) if the meter is in fact providing a pulse output. The logger I am using can support tansistor type/SO inputs but I am not registering any pulse even though there is flow through the meter. The manufacturer of this unit is no longer in business. Any guidance would be very much appreciated.





RE: NPN Open Collector
Ed
RE: NPN Open Collector
Ed
RE: NPN Open Collector
1k, 0.25w resistors are common for 5v circuits, but a 24v signal probably calls for a higher value of resistance (maybe 4.7k or 5k), but more complete info is required to be certain.
Another option would be to use a lower pull up voltage. Typically the receiver circuit would provide this anyway leaving only the open collected at the source end.
If it's just for a short test, it's less important.
But I'd still use 5k vice 1k to eliminate that small risk.
RE: NPN Open Collector
RE: NPN Open Collector
RE: NPN Open Collector
RE: NPN Open Collector
The meter does not say "24V+Max"
RE: NPN Open Collector
You may learn something by checking ohm readings between different pairs of terminals with no power applied.
RE: NPN Open Collector
Ed
RE: NPN Open Collector
RE: NPN Open Collector
RE: NPN Open Collector
There is no other power supply to the oil meter. I put in a 10k resistor across Pulse and Gnd, but I am still reading zero Volts. I also checked ohm readings between different pairs of terminals with no power supplied. Still no wiser!
@ markcraig
Checked Hz across all terminals..... no deviation from zero
RE: NPN Open Collector
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: NPN Open Collector
RE: NPN Open Collector