4–20 mA Loop Scaling

Flowmeter and instrumentation calculators

4–20 mA scaling, sensor ranging and loop budgets without the head-scratching. Built for the instrument techs and electricians who commission water plants.

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A worked example

4–20 mA current loop

Linear scaling + loop resistance budget

The figures shown are an indicative worked example. Every result Tenselo produces shows the inputs it used and the method behind it, so the work can be checked rather than taken on trust.

Inputs

Sensor range 0 – 10 bar

Loop supply 24 V

Loop resistance 250 Ω

Cable run 300 m

Results

0 bar

at 4 mA

10 bar

at 20 mA

0.625

bar / mA

600 Ω

Max loop R

12.5 V

Headroom

2-wire

Loop type

Why it matters on the job

Scaling that's right

Engineering units mapped to 4–20 mA so SCADA reads exactly what the sensor sees.

Loops that drive

Resistance budget vs supply checked so the transmitter has the headroom to work.

Signals that survive

Cable run, volt-drop and noise margins sorted before you energise.

Flowmeter pulse output and instrumentation calculations

Tenselo includes instrumentation calculators for water-meter pulse scaling, flowmeter installation, analogue signals, current loops and control-system sizing. Use the meter's configured output and the receiving instrument's input requirements when checking how a flow measurement will be displayed or recorded.

Flowmeter K-factor and pulse scaling calculator

INS-004, Flowmeter K-Factor / Pulse Scaling, converts pulse frequency to flow, flow to pulse frequency, or total pulses to volume. Its K-factor inputs use pulses per litre or pulses per cubic metre. Check whether the meter documentation instead states litres per pulse; that is the reciprocal convention and must be converted before entering a pulses-per-volume value.

Static worked example: a K-factor of 2 pulses per litre and a frequency of 20 Hz give 20 / 2 = 10 L/s, or 600 L/min and 36 m³/h. A total of 10,000 pulses at that K-factor represents 5,000 litres, or 5 m³. This example illustrates the scaling arithmetic; commissioning also requires the correct meter configuration and counter settings.

Flowmeter straight-length calculator

INS-005, Flowmeter Straight-Length, compares available upstream and downstream pipe runs with guidance based on meter type, pipe bore, upstream fittings and the selected flow-conditioner assumption. Treat the result as an installation check against stated assumptions. The exact manufacturer's instructions remain necessary; there is no single straight-length rule for every meter.

For preliminary meter size and output selection, use HYD-029, Water Meter Sizing. Size selection and signal scaling answer separate questions: a correctly scaled counter does not establish that the meter is suitable for the flow duty.

Analogue scaling and 4–20 mA loops

The catalogue also includes analogue signal scaling, 4–20 mA loop resistance budgeting, differential-pressure flowmeter square-root scaling and pressure-transducer range selection. Match each calculation to the signal type and instrument configuration.

New accounts require approval. These public descriptions and the static example explain the tools; running project calculations requires authorised application access. See availability and registration. Review instrument selection and commissioning with a competent person.

What is in this category

14 Instrumentation & Control calculators

Every calculator in this category, by its reference code. Running them requires an approved Tenselo account with access to the relevant calculators.

INS-001 4-20 mA Loop Resistance Budget

2-wire (loop-powered) transmitter: will the supply drive 4-20 mA through the sense resistor, barrier & cable?
INS-002 Analog Signal Scaling

Convert 4-20 mA / 0-10 V / 1-5 V / raw counts to/from engineering units, with PLC raw scaling (8/12/16-bit) & under-range
INS-003 DP Flowmeter Square-Root Scaling

Differential-pressure flow (orifice/venturi) where flow is proportional to sqrt(DP) - signal <-> flow with low-flow cutoff
INS-004 Flowmeter K-Factor / Pulse Scaling

Pulse-output flowmeter (turbine/paddlewheel/mag): K-factor -> flow rate & totalised volume, both ways
INS-005 Flowmeter Straight-Length

Upstream/downstream straight pipe a flowmeter needs for accuracy
INS-006 Level Sensor Range & Scaling

Measuring span, 4-20 mA scaling, resolution and top/bottom blanking
INS-007 Pressure Transducer Range Selection

Pick a sensor range from normal/surge pressure with good turndown and accuracy
INS-008 Control Transformer VA Sizing

Size a control/isolation transformer for the continuous (sealed) load and the inrush of the largest device
INS-009 Instrument Air Demand & Receiver

Air demand, receiver volume and compressor FAD for pneumatic actuators
INS-010 PLC I/O & Control Panel Power

I/O card count (with spares) and the 24 V DC panel supply
INS-011 RTU Solar / Battery Autonomy

Battery Ah and solar watts for an off-grid telemetry outstation
INS-012 VSD / Soft-Starter Selection

Drive & soft-starter sizing, start method vs DOL inrush (IEC 60947-4 / 61800)
INS-013 SCADA Poll / Scan Capacity

Scan-cycle time, channel utilisation and how many RTUs fit the poll rate
INS-014 Telemetry Data Budget

Monthly cellular data per remote site from poll rate and payload

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