One handheld tool that measures, sources and simulates almost every signal an instrument technician meets in a plant.
A multifunction process calibrator can measure and source current, voltage, resistance, frequency, temperature and pressure from one handheld unit. It replaces a bag full of separate meters and simulators during calibration and loop checks.
What Is a Multifunction Process Calibrator?
A multifunction process calibrator is a portable, battery powered instrument with two independent channels that can measure one signal while sourcing another. Technicians use it to check transmitters, switches, indicators and control system inputs against a known reference, as explained in instrument calibration terms.
Popular examples include the Fluke 725 and Fluke 726, along with similar models from Beamex, Additel and others. They are the everyday workhorse of most instrument maintenance teams.
On the Fluke 726, the DC current range is 24 mA with accuracy of 0.01 percent plus 2 µA. Its voltage range is 30 V with accuracy of 0.01 percent plus 2 mV.
It also measures resistance up to 4000 ohms and frequency up to 15 kHz. With external 750P modules, pressure accuracy reaches 0.025 percent.
Measure, Source and Simulate Functions
Source mode drives a known signal into a device, such as 12 mA into a control valve positioner. Simulate mode acts like a 2 wire transmitter, controlling loop current supplied by the DCS.
Measure mode reads the output of the device under test. Because both channels work together, you can source an input and read the output at the same time.
The Fluke 726 loop supply provides 24 V with up to 22 mA. That is enough to power a transmitter on the bench without a separate power supply.
7 Powerful Field Uses of a Multifunction Process Calibrator
Use 2 is covered in detail in our instrument loop checking procedure. Use 5 connects well with pressure switch set point and deadband testing.
Auto step and auto ramp functions speed up these jobs. The calibrator steps through 0, 25, 50, 75 and 100 percent by itself while you watch the response.
Transmitter Error Formula With a Worked Example
Error percent of span = (Measured mA minus Expected mA) ÷ 16 × 100
Worked example:
Range 0 to 10 bar, applied input 5 bar
Expected mA = 4 + 16 × (5 ÷ 10) = 12.00 mA
Measured mA = 12.04 mA
Error = (12.04 minus 12.00) ÷ 16 × 100
Error = 0.25 percent of span
Many multifunction calibrators calculate this error automatically in transmitter error mode. You only enter the range and the calibrator shows the error for each test point.
If the error exceeds tolerance, perform a zero and span adjustment or a sensor trim, then repeat the as left test.
Types of Process Calibrators
Measures and sources electrical, temperature and pressure signals.
Adds HART communication and automatic result upload.
Focused on mA source, simulate and measure only.
Specialized RTD and thermocouple simulation and measurement.
For sensor level temperature calibration you still need a heat source such as a dry block calibrator. The multifunction unit reads the sensor while the block holds a stable temperature.
Our guide on types of temperature calibrators explains how these tools work together. Documenting models that talk HART still need the proper loop resistance described in HART loop resistor basics.
Choosing between these types depends on plant size and how results are recorded. Small teams often start with a basic handheld unit and move to documenting models when audits demand paperless records.
Calibrator Comparison Table
| Tool | Electrical Signals | Temperature | Pressure | Best Use |
|---|---|---|---|---|
| Multifunction calibrator | Yes | Simulate and measure | With modules | Field calibration |
| Loop calibrator | mA only | No | No | Loop checks |
| Dry block | No | Generates heat | No | Sensor calibration |
| Dead weight tester | No | No | Primary standard | Pressure reference |
A dead weight tester remains the reference for high accuracy pressure work. The multifunction unit is faster and more practical in the field.
Most technicians carry a multifunction calibrator and a hand pump together. That pair covers the majority of daily calibration jobs.
For thermocouple loops, the calibrator applies internal cold junction compensation automatically. Our article on cold junction compensation explains why this correction matters for every millivolt reading.
Accuracy, Traceability and Good Practice
A common rule is to keep a test uncertainty ratio of at least 4 to 1 between the calibrator and the device under test. For a transmitter with 0.1 percent accuracy, the calibrator should be about 0.025 percent or better.
Send the calibrator itself to an ISO 17025 accredited laboratory on a fixed interval to keep traceability. Record its certificate number in every calibration report.
Consider measurement uncertainty from leads, temperature and pressure modules as well. Let the calibrator warm up and use good quality test leads for stable readings.
Transmitter Error Calculator
Try a measured value below the expected current to see a negative error written as minus. This matches how most calibration sheets record low readings.
- One tool replaces several meters and simulators.
- Measure and source at the same time.
- Built in loop power and error calculation.
- Stored results simplify documentation.
- Needs external modules for pressure.
- Cannot generate temperature for sensor checks.
- Requires regular recalibration for traceability.
- Precision models are costly.
Fluke 726 Users Manual PDF
Process Calibrator Demonstration Video
Multifunction Process Calibrator FAQ
Related Articles
- Types of Temperature Calibrators
- Dry Block Calibrator
- How to Calibrate a Pressure Sensor
- How to Calibrate a Temperature Transmitter
- Calibration Interval Determination
External References
- Fluke 726 Precision Multifunction Calibrator, Fluke
- Fluke 725 Multifunction Process Calibrator, Fluke
- Multifunction Calibrators, Fluke
- 726 Users Manual, Fluke
- Calibration, Wikipedia
What We Learn Today
- This calibrator measures and sources nearly every field signal from one handheld unit.
- Transmitter error is the difference between measured and expected mA as a percent of span.
- Keep a 4 to 1 accuracy ratio and send the calibrator for traceable recalibration.