Flow meter acquisition | How to transmit the signal of the flow meter to the PLC and display it on the computer screen without flow rate

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1. How to read the pulse signal of a flow meter? The method of reading the pulse signal cracking number of a flow meter mainly depends on the type of signal and the reading equipment used to read it. The core is to convert the flow value by counting the pulse frequency or quantity.

Firstly, signal type recognition requires confirmation of the electrical characteristics of the flowmeter pulse output.

1. Open collector circuit (NPN/PNP): The most commonly used and requires external power supply (usually 12-24VDC), with a level jump during the pulse (NPN pulse pulls down to 0V, PNP pulls up to the supply voltage).

Voltage pulse: Directly output 5V/12V/24V level pulses 3. NAMUR: Intrinsic safety type, needs to be used in conjunction with isolation barriers 4 Relay contacts: mechanical contacts for on/off, no polarity requirements but low frequency

2. Hardware connection scheme: Select the matching reading device according to the signal type: • PLC high-speed counter: the most commonly used scheme, supporting frequencies above 100kHz (such as HSC of Siemens S7-1200) • Pulse collection module: RS485/Ethernet pulse module (such as Advantech ADAM-4080) can be selected for IoT applications • Single chip microcontroller acquisition: Arduino/STM32 reads through interrupts or external counters (requires level matching circuit) • Special display instrument: matched with flow integrator to directly display cumulative flow

3. Key parameter settings: Three core parameters must be configured before reading

1. Pulse equivalent (K coefficient) Each pulse represents a flow rate value (e.g. 1 pulse pulse duration=0.1 liters), refer to the flowmeter manual for 2 Signal filtering time: to prevent accident

al triggering caused by mechanical vibration (usually set at 10-50ms) 3. Sampling period: integration time for instantaneous flow calculation (recommended 1-10 seconds)

4. Practical operation example (taking Siemens S7-1200 PLC as an example) 1 Hardware wiring: NPN pulse signal is connected to the DI point of the PLC (such as I0.0), and the common terminal is connected to the 24VDC positive terminal. 2. Configuration configuration: Enable HSC1 in the Botu software, and select the "frequency measurement" mode. 3 Program development://Read the instantaneous frequency value L "HSC1". CV//Obtain the count value T # TempValue//Convert the flow value L # TempValueL Pulse_K//Pulse equivalent * R T # FlowRate4. Calibration verification: Use a standard flow source to send fixed pulses and check the displayed value

V. Precautions • Electrical isolation: Industrial sites must be equipped with signal isolators to prevent electromagnetic interference • Impedance matching: Voltage type signals must ensure input impedance>100k Ω • Frequency limit: Mechanical flow meters pulse frequency is usually<10Hz, turbine flow meters can reach several kHz • Safety warning: Intrinsic safety equipment must be used in explosion-proof areas, and direct connection to non explosion-proof collectors is strictly prohibited. Refer to the latest industry standard GB/T 32201-2015 "Gas Collectors The pulse output parameters of the flowmeter must meet the requirements of signal amplitude>4V (when the load is 1k Ω) and rise/fall time<1 μ s. The actual acquisition error mainly comes from the accuracy of pulse equivalent calibration. It is recommended to use a high-precision frequency source (such as Fluke 725 calibrator) for on-site calibration.

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