Chatterbox pulse meter monitoring

Question

Hi, 
 
 I'm hoping someone has come across this before. 
 
 I have a Dresser Roots Chatterbox barrier which provides a current sinking connection for monitoring a gas meter 
 
 I also have a pulse acquisition meter which can work with dry contacts (done this successfully lots of times) 
 
 It can be set for dry contacts, or what it calls 'active pulse output' 
 
 it doesn't work either way. It sounds to me like the current sinking from the chatterbox isn't going to work with the meter, so I'm hoping someone has worked on these sort of systems before and can offer some advice 
 I have attached the wiring diagrams / all the info I have 
 PDF PDF

mapj1 · Answer

I have not used this exact kit, but here are a few thoughts to break it down. First, confirm that the two signal earths are happy being interconnected and there is not some unpleasant voltage offset either AC or DC between them - these are not fully floating contacts, but electronics pretending to be and depending on power arrangements they may not agree about the exact value of 0V. 
 Can you verify that the pulse counter is counting - perhaps by putting a pair of wires where the isolated contacts ought to go, and flicking the ends together a few times to see that a count, any count, is registered ? There needs to be a modest DC voltage between the ends of those wires, until they make contact, and then the voltage collapses, contact current limited by a pull-up resistor inside the counter. If you use your meter on the mA range to 'short' them, you can see the circuit current limit, and verify that internal resistor value. I'd expect 5V or so when open, and about half a mA to a few mA of short circuit current. 
 Then to look at the thing making the pulses. 
 With the meter on the ohms range, connected to the output of the sensor, assuming the meter is is fast enough, when it is reading, you should see it flick between the two states that represent on and off. 
 I see they note that the output is not a perfect zero ohms, but rather a very high impedance for off and about 100 ohms for on, and that polarity will be very important - negative earth. 
 It may be that the 100 ohms on -resistance is not pulling it low enough to be registered as an 'on' by the counter- but a test with the open wires and a 100 ohm resistor will prove that one way or the other. 
 It may be that the pull up voltage provided by the Rayliegh counter is too high or the wrong polarity for the on-off to register, but that is not so likely. At that point I'd be reaching for a scope, but I presume you do not have one to hand or you would alredy have done so. 
 Mike.

Chatterbox pulse meter monitoring

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