Measuring Instruments Selection Guide
Measuring instruments are divided by the quantity measured into groups such as multimeters, clamp meters, testers, power analyzers, oscilloscopes and thermometers.
This guide explains what to look at when choosing products in the Measuring Instruments category.
Which device group for which measurement
- Voltage, current and resistance. Digital multimeters for general measurements, and clamp meters for reading current without opening the circuit.
- Installation and device tests. Under electrical and electronic testers you find RCD and socket testers, voltage and continuity testers, phase sequence meters and cable tracers. The insulation resistance testers in the same group measure insulation at test voltages such as 250 V, 500 V and 1000 V; for earth resistance, earthing measuring instruments are in a separate category.
- Energy and power. Power quality analyzers, bench-type power meters and socket-type wattmeters are in the energy analysis instruments group.
- Electronics laboratory. Oscilloscopes, electronic measuring instruments including LCR meters and signal generators, and laboratory power supplies.
- Temperature. Infrared and probe thermometers and data loggers are under temperature and heat control instruments; thermal cameras, which show the heat distribution as an image, are a separate category.
- Environment and mechanical. Lux meters, anemometers, sound level meters and vibration meters are under environmental measuring instruments, and laser meters and alignment devices under laser measuring devices. Coating and thickness gauges are in their own subcategory, and tachometers are listed under process control instruments.
- Process. Temperature, current, voltage and loop calibrators are in the process calibrators group.
Mechanical workshop measuring tools such as calipers and micrometers are not part of this category.
Values to compare in the technical data
- Display count. This is the largest number the display can show and it determines the resolution. A 1999-count multimeter cannot show tenths of a volt when measuring 200 V and above; a 6000-count device shows up to 5999 on the display, so it gives the same detail up to 599.9 V.
- Accuracy. Written in the form ±(% reading + digits). On a device with ±(2%+2) accuracy, a display reading of 100.0 V can actually be between 97.8 V and 102.2 V. Because the digits allowance is fixed, the relative error grows for readings at the low end of the range; choose the range closest to the value to be measured.
- True RMS. Devices that work on the average value measure only a pure sine wave correctly; True RMS devices also measure a distorted wave correctly. This feature matters in installations with nonlinear loads such as variable frequency drives, electronic ballasts and computers.
How to read the measurement category label
The label gives the category and the voltage valid in that category together: for example CAT III 600 V. The categories are defined in the IEC 61010 safety standard series, and at the same voltage a higher category means a higher withstand against transient overvoltage: for 600 V this value is 6000 V in CAT III and 8000 V in CAT IV. A device can state two values at once (for example CAT III 1000 V / CAT IV 600 V); each voltage is valid for its own category.
Probes and test leads also have their own category and voltage rating; when choosing measuring instrument accessories, this rating is evaluated together with that of the device. Which category is required is determined by the measurement point, the project and manufacturer data.
Brand and order notes
- Unit model codes begin with prefixes such as UT, UTG, UPO, UTi, UDP and LM depending on the product group; you can use the code in the product name (for example UT204+, UTi120B) in the search.
- Products are sold by the piece.
- Some of the products are listed as made to order; for these the lead time is confirmed before the order.
Measuring and Test Instruments Comparison Table
| Instrument Type | Measured Parameters | Key Technical Feature | Typical Application | Category Link |
|---|---|---|---|---|
| Digital Multimeter | AC/DC Voltage, Current, Resistance, Capacitance, Continuity | True RMS · CAT III / CAT IV safety rating | Panel troubleshooting, PCB diagnostics and sensor verification | Multimeters |
| Digital Clamp Meter | Non-contact AC/DC Current (A), Voltage, Frequency | Current measurement via jaw without breaking the circuit | Phase load balancing, motor running current and PFC checks | Clamp Meters |
| Insulation (Megger) & Earth Tester | 250V–1000V Insulation Resistance (MΩ/GΩ), Earth Resistance | High-voltage dielectric integrity testing | Cable, motor winding and facility earthing acceptance tests | Electrical and Electronic Test Instruments |
| Thermal Imager & Environmental Meters | Temperature profile (°C), Lux, Sound, Distance | Non-contact hotspot and loose terminal detection | Predictive panel maintenance, breaker and busbar thermal audits | Measuring Instruments |
Frequently asked questions
What is the difference between a multimeter and a clamp meter?
A multimeter measures current by being connected in series with the circuit; this requires the circuit to be opened, and the current that can be measured is limited by the device's current input. A clamp meter closes its jaws around the conductor and measures currents at the level of hundreds of amperes without interrupting the circuit. A multimeter is used for precise measurement of small currents and for electronics work, and a clamp meter for panel and motor currents; in the field both are often found together.
When is a True RMS measuring instrument needed?
It is needed when the measured current or voltage is not a pure sine wave. Nonlinear loads such as variable frequency drives, electronic ballasts and computers draw current in short pulses. A device that works on the average value can read up to 40% low or up to 10% high on this waveform. A True RMS device measures the effective value correctly even on a distorted wave.
What is the difference between CAT III 600 V and CAT IV 600 V?
CAT III covers measurements in the building installation, that is, distribution panels, circuit breakers and fixed wiring. CAT IV is for measurements at the source of the installation: meters and main overcurrent protective devices. Even though the voltage value is the same, the transient overvoltage the device must withstand is different; for 600 V it is 6000 V in CAT III and 8000 V in CAT IV.
Can insulation resistance be measured with a multimeter?
No. The multimeter's resistance range measures with a low voltage and cannot test insulation weaknesses at the megohm level under conditions close to the operating voltage. An insulation resistance tester (megohmmeter) makes the measurement with a selectable DC voltage such as 250 V, 500 V or 1000 V. The test voltage and acceptance value are determined according to the installation, the project and the relevant standard.
What is the difference between an infrared thermometer and a thermal camera?
An infrared thermometer gives the average surface temperature of the targeted area as a single number. A thermal camera makes the same measurement for every point of the image and shows the temperature distribution as a picture. To look for which connection in a panel is heating up, a thermal camera is more practical; to monitor the temperature of a known point regularly, an infrared thermometer is.