I need help figuring out how to connect the (pulse-based) output from a flow sensor to a safety barrier
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This post was last edited by cooldick on 2017-11-3 at 20:40. Dear experts: I’ve come across a flow meter whose manual states that the pulse output is of the open-collector transistor type (with a wiring diagram provided). I was wondering whether, if this flow meter is connected to a safety gate, it would be sufficient to use a safety gate with a NAMUR switch as the input and a transistor as the output; the output from the safety gate could then be connected to the PLC’s high-speed pulse counter. This is the first time I’ve encountered such a situation – usually, proximity switches are used directly in these cases. (Optically isolated open-circuit collector output, 5 to 30 VDC power supply; maximum current of 40 mA at 30 VDC. The output voltage drops to 1.8 VDC when the current is 50 mA, and to 1.6 VDC when it is 10 mA.) Thank you very much for your response!
What brand is your flow meter? From the picture I can see, it seems that the frequency output of the flow meter is passive; also, can the pulse output be fed directly into a pulse card?
It’s a NUFLO flow meter imported from abroad, used in areas with explosion hazards; therefore, an isolation barrier is necessary. But when choosing such a barrier, I was confused – they all have dry contact or proximity switch inputs. What does that even count as? . . .
This post was last edited by tiger2010 on 2017-11-4 07:22. So far, I have not encountered situations where pulses/frequencies also need to be isolated using isolation gates; referring to the documentation from P+F and Nanjing Youbei, the isolation of pulse/frequency signals and digital signals is a matter of isolating two different types of inputs
I’m not quite sure; at the factory, the high-precision device used for loading the goods connects the pulses directly to the PLC, without any isolation barrier
{:2_36:} Yes, this sensor still requires power from a safety barrier; if that’s not possible, we’ll have to consult the sensor manufacturer first
Well, looking at that \"open collector pulse input\" option in the lower right corner of the image, doesn’t your flow meter come without this converter? This thing doesn’t mean that the user has to provide their own input port, right?
The power supply manufacturers are not included in the ones in the lower right corner and at the top; they need to be purchased separately. The component in the lower right corner is likely the pulse acquisition module
I remember that the Gaozhun mass flow meters seem to have a pulse output, and the Emerson systems are connected directly to the system
It is possible. The NAMUR input is active; if a safety gate with an open-circuit collector output is used, it is necessary to ensure that the input on the PLC side is also active. It is also important to verify that the output frequency range of the flow meter falls within the range accepted by the safety gate. After installation, it must be confirmed that the safety gate can receive all the pulses sent by the flow meter, meaning that the wires will not affect the frequency output