Water meter & PLC

hashem

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Join Date
Aug 2005
Location
anytown
Posts
33
I have water meter equiped with optoelectronic pulser as follow:
Switch type: IR reflex light barrier to DIN 19234; plug-in design
Switch voltage: 8.2 VDC
Switch current: < 1.2 mA
Quiescent current: > 2.1 mA
Can I wire the pulser output directly to PLC input 24VDC?
Any suggestion will be appreciated.
 
24V dc​
1746-IB8 Input 8 Current Sinking DC Input 19

24V dc​
1746-IB16 Input 16 Current Sinking DC Input 19

24V dc​
1746-IB32(1) Input 32 Current Sinking DC Input 19

24V dc​
1746-ITB16 Input 16 Fast Response DC Sinking Input 19

24V dc​
1746-IV8 Input 8 Current Sourcing DC Input 22

24V dc​
1746-IV16 Input 16 Current Sourcing DC Input 22

24V dc​
1746-IV32(1) Input 32 Current Sourcing DC Input 22

24V dc​
1746-ITV16 Input 16 Fast Response DC Sourcing
Specification Catalog Number
1746-IB8 1746-IB16
(RTB)
1746-ITB16
(RTB)
(Fast Response)
1746-IB32​
(1)

Voltage Category​
24V dc sink

Operating Voltage​
10 to 30V dc sink 15 to 30V dc at 50°C sink

15 to 26.4V dc at 60​
°C sink

Number of Inputs​
8 16 16 32

Points per Common​
8 16 16 8

Backplane
Current Draw
5V dc​
0.050A 0.085A 0.085A 0.050A

24V dc​
0.0A 0.0A 0.0A 0.0A

Signal Delay (max.)​
on = 8 ms

off = 8 ms
on = 8 ms
off = 8 ms
on = 0.3 ms​
(2)

off = 0.5 ms
on = 3 ms
off = 3 ms
Off-State Voltage (max.)​
5V dc 5V dc 5V dc 5V dc

Off-State Current (max.)​
1 mA 1 mA 1.5 mA 1.6 mA

Nominal Input Current​
8 mA at 24V dc
Specs are the answer my friend, you can get them for all of the AB discrete I/O modules by going to AB.com and looking them up. If you are using some other brand, then do the same thing on their site. As you can see, the switching voltage ranges for these 24V modules would not suit your 8.2VDC device. Maybe another module would be more appropriate?

 
Thank you randylud.
Anyone could give me informatin source regarding IR reflex light barrier to DIN 19234 (namur)?
Thank you in advance.
 
It is an "Optoelectronic IR reflex light barrier".
But the voltage and current specs seems to indicate that it mimics a NAMUR type sensor.
So you need a NAMUR/DC converter to get the signal into the PLC.
 
Thank you JesperMP.
Anybody know device that could convert from NAMUR level to PLC 24VDC logic?
With thanks.
 
PR Electronics has the 2288 module that converts/isolates between many different signal levels incl. NAMUR. I use it myself.
There is an additional nifty "pulse stretching" function that may be useful if the impulse from the sensor is so short that the PLC cannot pick it up.
Tip: Put the converter locally in a terminal box if the cable runs are very long. Otherwise it will pick up noise and convert it to false signals.
 
Thank you JesperMP again.
Cause you deal with this kind of sensor, can I wire the sensor as the attached image?
:whistle:
namur.jpg
 
I never try to do like that. From where did you get that diagram ?

I know that NAMUR defines a supply voltage (8.2V) and OFF and ON levels in current (1.2mA and 2.1mA).

I guess that the diagram applies to a particular kind of PLC input card. I doubt that it will work everywhere.
Some counter inputs will accept a NAMUR sensor directly.
 
Jesper,
The diagram was drawn by me, it is for any traditional 12-24VDC PLC input which has the following specifications:
ON Current/Voltage Level: >5mA/10VDC
OFF Current/Voltage Level: <0.5mA/<2VDC
From the diagram: 24V=8.2V+10V+5mA*R
R=1.16K
IOW, R will achieve ON current>2.1mA and 8.2V
I am not satisfied if it will work or may damage the sensor and/or PLC input!
What is your opinion and advice.
With thanks
 
hashem,
I have absolutely no idea if it will work or not.
I would not waste any time but get an signal conditioner that is designed to do the job.
But I am not you.
 
Thank you OkiePC,
The PLC input as the following diagram still work ON/OFF logically.
Pulser.jpg

I am not satisfied if I add the pulser it will work or may damage the sensor and/or PLC input!
What is your opinion and advice.
PLC input impedance: 1.8K @12-24VDC
With thanks
 
I agree with Jesper. Get a signal isolator/conditioner designed for your sensor. I don't think a simple voltage divider circuit will do what you intend without risk to the sensor.
 
Here's a link discussing signal isolation to a NAMUR standard signal

LINK to Tekron

If you're device is in a hazardous area, then use intrinsically safe barriers that limits the current going to the sensor.

Non-hazardous? You can use a simple non-isolating interface by using a single, general purpose, 2N2222 transistor to interface an 8-volt NAMUR device and connect directly to a 24-volt PLC input.

Here is a good resource on simple transistor circuits:

LINK PCB Heaven

Hope this helps.

-Chris
 
Last edited:

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