Correct precision calibration resistors are costly and often cumbersome, usually in a big field or can. These are overkill for low-cost handheld digital multimeters (DMMs) and LCR Meters, particularly when used as a “sanity test” earlier than making vital measurements.
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More often than not, I’d use a precision axial-leaded resistor for this function. Nonetheless, I considered making one thing extra handy that offered the precision resistor with some mechanical safety to instantly plug right into a DMM or LCR meter. If utilizing a high-resolution bench DMM like a Keysight KS34465A or Keithley DMM6500, usually you need to know the resistor temperature in addition to the resistance worth, and the thought got here to thermally hyperlink the precision resistor with a precision thermistor for this function. Within the spirit of low-cost DIY, the thought to hyperlink the axial-lead precision resistor with an axial-lead precision thermistor with a brief part of warmth shrink tubing appeared cheap, and you’ll’t get a lot easier or cheaper than the idea proven in Determine 1!
Determine 1 Linking an axial-lead precision resistor and an axial-lead precision thermistor with a brief part of warmth shrink tubing.
I nonetheless wanted mechanical safety for the resistor/thermistor combo, and the right way to make direct DMM connections. An ordinary twin banana plug is an effective host for the combo, however solely has two connection terminals. Utilizing a 3D printer, I created a customized 3D printed “plug” to help the thermistor leads as proven in Determine 2.
Determine 2 A customized, 3D-printed “plug” helps the thermistor leads, permitting for a resistor/thermistor combo with mechanical safety.
Determine 3 reveals the resistor/thermistor combo mounting scheme, the place the precision axial resistor leads are inserted into the twin banana plug holes and secured by the plug’s inner screws (go away some slack within the resistor results in assist scale back mechanical stress on the precision resistor). Word how the resistor lead ends are looped over, creating small terminals for exterior “clip lead” or “Kelvin clips” measurements. The axial thermistor leads are threaded by the customized 3D printed plug and loop on the high.
Determine 3 The resistor/thermistor combo mounting scheme, the place the precision axial resistor leads are inserted into the twin banana plug holes and secured by the plug’s inner screws.
General, the idea creates a small compact holder for the precision resistor and thermistor combo with handy connections to the resistor measurement instrument instantly by the twin banana plug. Temperature measurements use small clip results in the thermistor leads, which protrude from the highest of the twin banana plug and a customized 3D printed plug high, as proven in Determine 4.
Determine 4 A resistor temperature studying exhibiting the small clip results in the thermistor leads, which protrude from the highest of the twin banana plug and customized 3D printed plug.
When utilizing this setup, I discovered the bench-type DMMs just like the DMM6500 have banana enter terminals 3~3.5 °C hotter than ambient (the KS34465A was 2~3 °C hotter). This helps clarify the lengthy settling time for bench DMM new banana connections to stabilize, the place differential thermal EMFs can corrupt delicate measurements. Handheld DMMs appear to stabilize a lot faster for the reason that inner handheld temperature is barely above ambient, whereas the bench DMMs are a lot hotter.
Anyway, I hope some people discover this DIY Precision Resistor with built-in thermistor idea handy and helpful, though wouldn’t advocate this for precision resistors beneath ~100 Ω, that is 4-wire Kelvin territory, and definitely not thought of “Metrology Certified.”
Michael A Wyatt is a life member with IEEE and has continued to take pleasure in electronics ever since his childhood. Mike has an extended profession spanning Honeywell, Northrop Grumman, Insyte/ITT/Ex-elis/Harris, ViaSat and retiring (semi) with Wyatt Labs. Throughout his profession he gathered 32 US Patents and up to now revealed a couple of EDN Articles together with Greatest Thought of the Yr in 1989.
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