Which signal type does your sensor use?
Analog sensors for fuel, pressure, load and temperature send their value as a voltage or a current. A signal with a live zero, such as 4-20 mA or 0.5-4.5 V, lets the device tell a true zero from a broken wire.
| Signal | Zero | Full | A reading outside the range means |
|---|---|---|---|
| 4-20 mA | 4 mA | 20 mA | 3.6 mA or less, or 21 mA or more: failure (NAMUR NE 43) |
| 0-20 mA | 0 mA | 20 mA | A zero reading cannot be told from a broken wire |
| 0.5-4.5 V | 0.5 V | 4.5 V | Below 0.5 V or above 4.5 V: open or short circuit |
| 1-5 V | 1 V | 5 V | Below 1 V: likely a broken wire |
| 0-5 V | 0 V | 5 V | Zero and a broken wire look the same |
| 0-10 V | 0 V | 10 V | Needs a divider on a 5 V input |
How does linear scaling work?
The value moves in a straight line between the two ends of the signal.
How do you calibrate from two points?
A datasheet range assumes a perfect sensor and a perfect install. Two real points remove the offset and gain errors of your own setup.
Read the low point
Empty tank, no load or zero pressure. Note the signal.
Read the high point
Full tank or a known load near the top of the range.
Check the middle
One more known value in the middle shows whether the sensor is linear.
Enter the gain and offset
Put m and b in the platform or the device configuration for that input.
How do you size a divider or a shunt?
The device input has a maximum voltage. A divider scales a higher sensor voltage down to it, and a shunt resistor turns a loop current into a voltage.
How do you spot a broken wire?
A reading outside the signal range is a wiring warning, not a value.
- 4-20 mA: 3.6 mA or less, or 21 mA or more, is a failure signal under NAMUR NE 43. Between 3.8 and 20.5 mA is still a measurement.
- Voltage signals: the tool treats a reading beyond your tolerance as an open or short circuit.
- Set the platform to flag these readings instead of plotting them as values.
Assumptions and limits
- The sensor is treated as linear. A non-linear tank or sensor needs a calibration table with more points.
- The device input range, ADC resolution and shunt are your inputs. The starting values are typical examples, not Tracom specifications. ST100 (published): 4 analog inputs and 5 AD inputs. Their input range and ADC resolution are not published, so take them from the datasheet.
- Resistor tolerance and input impedance of the device shift the divider slightly. Two-point calibration removes most of it.
- NE 43 values as summarised in the Wikipedia current loop article. The current edition of NE 43 is dated 2021-07-26 (NAMUR notice) and is available only from the NAMUR office, so the values could not be read in the official text. Last checked 2026-11-03.
Check the fault thresholds against the NAMUR NE 43 recommendation and the sensor datasheet before you set alarms on them.