The Analog Signal Values Calculator converts between raw sensor output and engineering units for 4-20mA current loops and 0-10V voltage signals. Instantly find the process value at any signal level or the signal output for any engineering unit value within the sensor range.
16
mA / V
100
EU
50
%
50
EU
8
mA / V
16
mA / V
100
EU
50
%
50
EU
8
mA / V
The calculator for analog signal values converts between raw signal measurements (mA or volts) and actual engineering unit values (pressure, temperature, flow, level) for 4–20 mA current loops and 0–10 V voltage signals — the two dominant analog signal standards in industrial instrumentation and process control.
The 4–20 mA current loop is the industrial automation standard for sensor signal transmission, mapping linearly: 4 mA = minimum process value (0% of span) and 20 mA = maximum (100% of span). The live-zero at 4 mA provides three key advantages:
The linear conversion: Process Value = (Signal − 4 mA) / 16 mA × Span + Minimum. Use this online calculator for any sensor range and signal level combination.
Voltage signals (0–10 V or 0–5 V) are common in HVAC controls and building automation. The linear mapping: Process Value = Signal (V) / 10 V × Span + Minimum (for 0–10 V). Voltage signals are more susceptible to noise and cable resistance voltage drop than current loops, making them less preferred for long cable runs over 30 meters or in electrically noisy environments. The resistor color code calculator helps identify the 250 Ω shunt resistor used to convert 4–20 mA to 1–5 V for PLC analog inputs.
PLC systems typically represent analog signals as raw integer counts (e.g., 3277–16384 for 4–20 mA on a 15-bit card). Engineering unit conversion uses the same linear interpolation: Engineering Value = (Raw count − Raw_min) / (Raw_max − Raw_min) × Span + Min_EU. Incorrect scaling parameters in PLC code are a frequent source of process control errors — a misconfigured temperature range causes controllers to behave incorrectly even when all hardware is functional. This calculator provides the forward and reverse conversions needed to verify PLC scaling.
Analog signal monitoring includes watching for fault conditions:
The temperature sensors calculator and electronics component calculators provide related instrumentation tools.
The calculator uses linear interpolation to map the measured signal value to the corresponding process value. First, the signal range minimum and maximum are determined by the selected signal type (e.g., 4 mA and 20 mA for 4–20 mA). The percentage of span is computed as % = ((signal_value − S_min) / (S_max − S_min)) × 100. The process value is then found as PV = P_min + (% / 100) × (P_max − P_min). This assumes a perfectly linear relationship between signal and process variable, which is the standard assumption for analog transmitters.
A percentage of span near 0% means the process variable is at or near its minimum range value; near 100% means it is at maximum. For 4–20 mA, a reading below 4 mA indicates a fault condition (open circuit or failed transmitter). A reading above 20 mA (typically up to 21.75 mA is allowable per NAMUR NE 43) may indicate an over-range or fault. Always verify that the measured signal is within the valid range for your transmitter and signal type before trusting the process value reading.
Inputs
Results
A 12 mA signal (midpoint of the 4–20 mA range) corresponds exactly to 50% of span, which is 100°C on a 0–200°C transmitter.
Inputs
Results
18.4 mA is 90% of the 4–20 mA span, giving 9.0 bar on a 0–10 bar transmitter.
The 4 mA live zero allows detection of open-circuit faults and power loss. If the signal drops to 0 mA, the system knows it is a fault condition rather than a valid zero process reading. This is a critical safety feature in process control.
EU stands for Engineering Units — the physical unit of measurement for the process variable (e.g., °C, bar, m³/h, %). You enter the minimum and maximum process values in whatever unit your transmitter is calibrated to, and the result will be in those same units.
Yes. For example, a temperature transmitter ranged 50–150°C with a 4–20 mA output would use process_min = 50 and process_max = 150. The linear interpolation works correctly for any range, including negative values.
NAMUR NE 43 is a recommendation that defines fault indication levels for 4–20 mA transmitters. It specifies that signals below 3.6 mA or above 21.0 mA indicate fault conditions, and signals between 3.8–4.0 mA or 20.0–20.5 mA indicate under/over-range conditions. This standard helps distinguish genuine process extremes from instrument faults.
The 4–20 mA current loop is superior for long cable runs because current is constant throughout the loop regardless of cable resistance (within limits). Voltage signals suffer from voltage drop across cable resistance, which introduces measurement error proportional to cable length and resistance. For distances over 100 meters, 4–20 mA is strongly preferred.
Apply the same linear scaling formula. For a 12-bit ADC (0–4095 counts) representing a 4–20 mA input, the equivalent counts for 4 mA and 20 mA depend on your module's specification (commonly 0–4095 or 3277–16383 for 16-bit). Substitute the count range for S_min/S_max in the formula: PV = P_min + ((count − count_min) / (count_max − count_min)) × span.
Common causes include: open circuit (reads below 4 mA or 0 mA), short circuit, excessive loop resistance causing voltage to fall below transmitter's minimum supply voltage, ground loops introducing noise offsets, transmitter miscalibration, or a faulty analog input card. Always check loop supply voltage and total loop resistance when troubleshooting.
For standard analog transmitters, yes — the output is designed to be linear with the process variable. However, some transmitters (particularly for non-linear sensors like thermocouples or RTDs) apply internal linearization so that their 4–20 mA output is linear in engineering units even though the underlying sensor characteristic is non-linear. Always consult the transmitter datasheet.
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