This document describes the field test and calibration method for temperature for the 61-310 and 61-312 DMMs. Most low-cost instruments and multimeters that measure temperature use thermocouples (TC). Thermocouples are an inexpensive method of measuring temperature. The accuracy of TC can range from 2% to as high as 20% depending on the purity of the metals and construction, so the better the accuracy the higher the cost of the TC. The TCs that come with low-cost instruments are normally of low accuracy, typically 5% or more. One nice fact is that regardless of the construction of the TC, if it is being used in normal environmental conditions the error can be compensated for. One typically overlooked fact is that water freezes at 32°F or 0°C and boils at 212°F or 100°C with very little error due to impurities of the water and barometric pressure. This can provide a typical user an easy to construct calibration standard of suitable accuracy. Fill one of those plastic thermal glasses that you have with crushed ice and add enough water to create the consistency of a slushy. At the same time bring a small pan of water to a boil. Remember that pure water will work best for this experiment. There are TCs that are constructed to be submerged in water but most TCs that are packaged with low-cost instruments come with a bead style TC which should not be used in liquids. If you have a bead type TC use something like a freezer bag or high temperature plastic wrap around the TC. Now all you need to do is make the measurement.
This document provides a method for calibrating the temperature measurement function of Ideal 61-310 and 61-312 Digital Multimeters (DMMs). It explains that low-cost thermocouples often have significant error, but this can be compensated using standard reference points: the freezing point of water (32°F / 0°C) and the boiling point of water (212°F / 100°C).
The guide details specific performance test ranges for both models, listing expected source values versus acceptable reading limits. It also provides step-by-step instructions for adjusting internal variable resistors (VRs) to calibrate the °C and °F scales using a temperature calibrator.
| Model Numbers | 61-310, 61-312 |
|---|---|
| Calibration Point (F) | 32°F +/- 1°F |
The document uses the freezing point of water at 32°F or 0°C and the boiling point of water at 212°F or 100°C as easy-to-construct calibration standards.
Set the rotary switch to "°C", connect a calibrator output of 0°C, and adjust VR2 for a display between -1°C and +1°C.
The expected source value is 750°C, and the acceptable reading range is between 722°C and 778°C.