Flowmeter Pulse Output Scaling Calculator
Set up a flowmeter pulse output for a PLC counter or totaliser: from maximum flow and pulse value find the pulse frequency, and check it against the pulse width and the input frequency limit.
- f = Qmax ÷ pulse value = 33.33 L/s ÷ 10 = 3.333 Hz
- Pulse width limit: f ≤ 1 ÷ (2 × width) = 10 Hz
- Allowed f = lower of width limit and input limit = 10 Hz
Pulse Output Formulas
Pulse width limit: f ≤ 1 ÷ (2 × tpulse)
Minimum pulse value = Qmax ÷ fallowed
Qmax is the maximum flow in L/s, the pulse value the volume per pulse and tpulse the on time of each pulse. With a fixed pulse width, the off time must be at least as long as the on time, which limits frequency to 1 ÷ (2 × width). The receiving input also has a maximum count frequency, often low for standard digital inputs.
Worked example
120 m³/h with 10 L per pulse gives 3.33 Hz, well within a 10 Hz input and the 10 Hz limit of a 50 ms pulse. With 1 L per pulse it would be 33 Hz, too fast for that input.
Frequently Asked Questions
What is a pulse value?
The volume (or mass) each output pulse represents, set in the flowmeter, for example 10 L per pulse.
Why does pulse width limit frequency?
Each pulse needs an on time and at least an equal off time. A 50 ms pulse cannot repeat faster than 10 Hz.
Pulse output or 4 to 20 mA for totals?
Pulses give an exact total with no drift; 4 to 20 mA integrated in the PLC gives a rate but the total accumulates small errors.
Learn more on the blog
4 to 20 mA current loop explained
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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