Open Collector Transistor to 1794 High Speed counter

best49erfan

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Join Date
Aug 2003
Location
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I have a water meter (badgermeter.com) that has a transmitter that its dc output is a open collector transistor. i need to get the pulse to a 1794-IP4 (flex IO 4 channel counter). i talked to their tech support and he said to take 24vdc to the switched input side with a 560 ohm resistor and same wire to the signal of the HSC. and the other side of the collector to common. I tried both the high and low inputs and do not have any counts on my plc. Any suggestions???
 
Model number please?

But in any case, the input of the 1794-IP4 is an optocoupler, so you would want to source it from the meter. Be sure to select a resistance that will keep you under the max for your meter's output, and be sure to fuse it.
 
Did the tech support know what you were connecting to it? The badgermeter has an optoisolated output. Looking at that Badger document, you will have a transistor collector on the meter connected to a photodiode input on the PLC. If you use a pullup resistor to 24V and wire it like tech support says, the current is going to be split betweeen the transistor and the opto on the PLC and there is no guarantee that it will split evenly (I guarantee it won't!) so there might not be enough current going through the opto to trigger your counter.

I would put the PLC opto input in series with the open collector and make sure the resistor was sized to not overload either the opto or the transistor. It would be easier if I could draw a diagram.

edit: I drew a quick sketch. Don't know how to insert photos on this site, but the link to my drawing is here. Hope it's legible :)
 
Last edited:
You'll need to provide a power source (a nine volt battery will do for testing) to supply power to the circuit.

As for connections:

Hook the positive side of the battery through your 560 ohm resistor (560 ohms will limit your current to 16 ma, which is more than enough) to terminal #5 of your meter.

Terminal #6 of your water meter will go to the positive input on your high speed counter.

The negative terminal on your HSC will connect to the negative side of your battery.

Should you find that the HSC already limits the current flow to your circuit to below 100 ma, then your don't need the 560 ohm resistor.
 
Here is how the tech told me how to wire it up.
Code: 
+24VDC from card-----------------------------Terminal 1 meter
                                      | R1
Signal wire from card------------------------Terminal 5
 
                                      -------Terminal 6
                                      |
COM from card--------------------------------Terminal 4

R1=560 ohm 1/2W

I also tried both signals (low and high) on card. Still not working. When I told him its going to a counter card he said he was not familiar with it, but thats how they wire them up.
 
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Is this tech from Badgermeter or the PLC rep?

What you describe is how we connect open-collector outputs to our non-isolated counter inputs (although our counters have the resistor built in). For an optoisolated input, it looks like rootboy's description of how to connect it agrees with what I was saying.
 
Lyndon A said:
Is this tech from Badgermeter or the PLC rep?

What you describe is how we connect open-collector outputs to our non-isolated counter inputs (although our counters have the resistor built in). For an optoisolated input, it looks like rootboy's description of how to connect it agrees with what I was saying.
Click to expand...


From Badger. Ok, going to try it now. I was not at work yesterday. Will let you know.
 
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best49erfan said:
Here is how the tech told me how to wire it up.
Code: 
+24VDC from card------------------------------------Terminal 1 meter
                                      | R1
Signal wire from card---------------------------------Terminal 5
 
                                      -------Terminal 6
                                      |
COM from card--------------------------------Terminal 4

R1=560 ohm 1/2W

I also tried both signals (low and high) on card. Still not working. When I told him its going to a counter card he said he was not familiar with it, but thats how they wire them up.
Click to expand...

Well, that won't work. Change what you have here to:

Code: 
+24VDC from card-------------------------------------------Terminal 1 meter
                            | R1       50ma
                            ---------  FUSE  --------------Terminal 5
 
                                 (HSC Neg)       (HSC Pos)    
                            --------------- HSC -----------Terminal 6
                            |
COM from card----------------------------------------------Terminal 4

And I would change R1 to at least a 1K resistor (you really don't need more than a few milliamps to trigger the HSC).
 
Actually, now that I have some coffee in me, his way of doing it should work...

Put a 1k ohm resistor in series with a LED between 5 (Positive) and 6 (negative). When the meter is not pulsing the LED will be on.
 
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rootboy said:
Actually, now that I have some coffee in me, his way of doing it should work...

Put a 1k ohm resistor in series with a LED between 5 (Positive) and 6 (negative). When the meter is not pulsing the LED will be on.
Click to expand...


his way is not working either.

on yours, you show the hsc neg and pos. do i use one of these and put the other to common?
 
Actually, his way is the standard way of doing things. I've gotta pay more attention to what I'm smoking. ;)

You will need to supply 12 - 24 volts to terminals 1 & 4 and it should just work.

You should check to make sure that there isn't anything there at the moment, but with the "12 - 24 VDC +" label, it implies that you have to provide it.
 
rootboy said:
Well, that won't work. Change what you have here to:

Code: 
+24VDC from card-------------------------------------------Terminal 1 meter
                            | R1       50ma
                            ---------  FUSE  --------------Terminal 5
 
                                 (HSC Neg)       (HSC Pos)    
                            --------------- HSC -----------Terminal 6
                            |
COM from card----------------------------------------------Terminal 4

And I would change R1 to at least a 1K resistor (you really don't need more than a few milliamps to trigger the HSC).
Click to expand...


This way is working! I tried his way, still no go.
 
Okay, so this has been bugging me all day. :confused:

But it finally occurred to me why the tech's method didn't work. He (and I), were assuming a high-impedance input to the HSC. I don't think that's the case, it makes more sense that it is a low-impedance path. So when the open-collector output was switched on, would make little to no difference to the input on the HSC (since it was already pulling itself to ground). That's why the series method would work while the pull-up method wouldn't.

In any case, that's my story, and I'm sticking to it... :whistle::ROFLMAO:
 

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