What this category covers
Calibration instruments supply a known value so that another instrument can be verified or adjusted. That is the whole distinction from the measurement categories, where the task is to read what a circuit or a process is doing. A multifunction calibrator that sources a current loop and reads it back belongs here; the meter that only measures it does not.
Because the value of any calibration rests on traceability, the specification conversation is about the reference rather than the instrument: the accuracy class of the standard, its stability over the interval between calibrations, and the uncertainty the whole chain carries. A calibrator that cannot be traced to a reference is not a calibrator in any useful sense - it is a source, and the difference matters the moment a result has to be defended.
The practical consequence is that the device under test comes first. Its tolerance, and the uncertainty the verification has to hold inside that tolerance, decide which reference class is needed, and everything else follows from there - the range coverage, whether the instrument has to source or read, and whether it can be carried to the plant or has to stay on a bench.
Product types in calibration & metrology
| Product type | How it works | Usually specified for |
| Pressure calibrator | A stable pressure source combined with a reference sensor of a higher class than the device under test | Field and workshop verification of transmitters, gauges and pressure switches, where one unit has to generate and measure |
| Calibration pump | Manual or pneumatic generation of pressure with a fine adjustment and a holding valve | Generating and holding pressure where the reference is provided separately, and where a simple rugged unit is preferred |
| Pressure test pump | Hand or motor driven pressurisation used to proof-test a component or a line | Pressure testing rather than calibration - a related duty that is frequently bought with the same accessories |
| Multifunction process calibrator | Sources and reads current, voltage, resistance and frequency, often with loop power and a built-in reference | Commissioning and maintenance rounds on transmitters, indicators and loops, where one instrument has to cover several signal types |
| Temperature calibrator | A metal block held at a controlled temperature, with a reference thermometer and often a second readout for the device under test | Field verification of thermocouples, RTDs and thermostats, where the probe can be inserted into the block |
| Temperature bath | A stirred liquid or fluidised medium provides a uniform temperature around the sensor | Laboratory work where the sensor is the wrong shape for a block, or where immersion depth has to match the application |
| Electrical calibrator | A precision source of voltage, current and resistance, sometimes with read-back of the device output | Bench verification of meters, recorders, input cards and transducers, where stability and traceability matter more than portability |
| Reference standard and thermometer | An independent, higher-accuracy device used as the comparison against which the working reference is checked | Establishing the reference for the working calibrator, and holding the traceability the whole chain depends on |
Fittings, hoses, adapters, seals and test leads are listed under this category too, and they are frequently where the error in a calibration actually enters.
How to choose a calibrator
There is rarely a single correct instrument for a duty, but there is always a
shortlist that can be justified and a set of answers that eliminates the rest. These
are the questions that decide it.
- The device under test and its tolerance, read first. Everything else in this category follows from how tight the verification has to be.
- The accuracy ratio between the reference and the device under test, which is what actually makes a calibration meaningful rather than merely recorded.
- Whether the calibrator has to source a signal, read one, or do both in the same operation, since the answer removes whole families.
- Range coverage, including the tolerance that applies at the working point rather than at the middle of the span where instruments usually look best.
- Portability against bench capability: a battery-powered unit for plant rounds, or a mains instrument with better stability for the workshop.
- The documentation required and the traceability the certificate has to show, because the record is often the deliverable rather than the reading.
- Whether the task is verification or adjustment, since a calibrator that also reads back the device output shortens the job considerably.
- The media and the connection involved for pressure work, including the fittings and seals that have to match the device under test.
- The recalibration interval of the reference itself, because a reference due for calibration is a reference that cannot be used.
Working through the selection in order
- Identify the device under test and the tolerance it has to hold.
- Set the uncertainty the verification has to achieve inside that tolerance, allowing a sensible margin rather than consuming the whole allowance.
- Choose the reference class that satisfies the uncertainty, and check the ratio between reference and device.
- Decide whether the calibrator has to source, read or both, and whether loop power is required.
- Establish the range coverage needed at the working point, not merely across the full span.
- Decide where the calibration happens, which settles whether the unit has to be portable or can remain on a bench.
- Confirm the connection and media requirements, particularly for pressure work where fittings and seals are part of the result.
- Agree the certificate and traceability requirement, then set the recalibration interval for the reference itself.
Comparing the technologies
| Approach | Best suited to | Limits | What it verifies |
| Pressure source with an integrated reference | Field verification of transmitters, gauges and switches with one portable unit | The reference class and the stability of the source together set what the unit can support, so a reference below the class the job needs limits the whole chain | Pressure instruments |
| Separate source and reference gauge | Where the reference has to be of a higher class than any integrated option provides | More items to carry, each with its own calibration interval and certificate | Pressure instruments |
| Electrical source with read-back | Loops, transmitters, indicators and input cards, and the connection between field and control system | Needs the correct lead arrangement, and lead resistance has to be allowed for rather than ignored | Electrical and process signals |
| Dry-block temperature source | Field verification of probes, thermostats and switches | Axial uniformity along the block and the fit of the probe inside it influence the result as much as the setpoint | Temperature sensors and thermostats |
| Stirred bath | Laboratory work, or sensors that cannot be inserted into a block | Bulkier to move, needs a medium, and takes longer to reach a stable condition | Temperature sensors |
| Deadweight tester | Establishing pressure as a fundamental reference rather than checking a working instrument | Manual operation, sensitive to levelling, and limited to the mass set available | Pressure reference |
Parameters to confirm before ordering
What is left after the technology is chosen is a list of values that only the
installation can supply. These are the ones that change the model, the price or the
lead time:
- The device or devices to be calibrated, with their tolerance and stated accuracy class.
- The uncertainty the verification has to hold inside that tolerance.
- The ranges and the working points, since the requirement at the working point governs rather than the full span.
- The signal types involved, and whether the calibrator has to source, read back, or both.
- Whether the calibration is carried out in a workshop or in the plant, and how the instrument is transported.
- The medium and the connections required, including fittings, seals and hoses for pressure work.
- The certificate and traceability requirement, and the form the record has to take.
- Whether the reference has to be recalibrated by a third party, and the interval the system expects.
- Whether the task is verification or adjustment, and whether the device output also has to be read.
- Quantity, and whether the requirement covers one bench or several maintenance teams.
Figures are quoted, not assumed
Specifications vary by model and application, so no performance figure is stated on
this page. Where a parameter has not been documented for a particular model, the
product page says so rather than filling the gap with a plausible number. Send the
values above and we will return the ones the selected model actually holds.
Where these instruments are used
