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Dmm dvm tester checker calibrator voltage reference
Provided on the small (2.1" x 1.6") circuit board are three separate circuits:
1. A 5VDC voltage reference that is accurate to within 0.01% (plus or minus 500uV) for a minimum of 6 months.
2. A 1.000mA DC current source that is accurate to within 0.1% (plus or minus 1uA)
3. Three 0.1%, 25ppm resistors - 1K, 10K, and 100K
An external power supply is not needed; The included 9V battery makes the unit self-contained and easily transported. An on-board on/off switch allows you to maximize battery life when not in use. Reverse polarity protection is included, so even if the battery is placed in the holder backwards no damage will result. A high brightness, low current LED clearly indicates when the reference is turned on.
The construction of the 5VDC reference circuit is very similar to what was described in my article in the September 2007 issue of Nuts and Volts magazine, "Build a .01% Accurate Voltage Reference" http://nutsvolts.texterity.com/nutsvolts/200709/?folio=52.
After the DMMCheck is assembled, it is powered up with a 9V power supply for a minimum of 200 hours to "age" the reference and improve its long term stability. After aging, the trim potentiometer is carefully adjusted for a reference output of 5.0000V as measured by our calibrated 8.5 digit HP 3458A DMM that has an accuracy of 0.0008%. (Davis Calibration, Certificate of Calibration # 3846118 valid through January 27, 2011). Accidental movement of the trimpot adjustment is prevented by the application of a small amount of clear nail polish. The ambient temperature is also recorded (typically 68oF). The circuit board was designed to minimize the effects of mechanical stress on the voltage reference IC. Specifically, the reference is placed on the edge of the circuit board and 2 adjacent slots decouple stresses in the board from reaching the reference which could otherwise cause the output voltage to shift.
1K, 10K, and 100K precision, low-drift resistors, connected in series are available to check the resistance function of your DMM. Depending on how you connect your meter leads, the following precision resistances are available: 1K, 10K, 11K, 100K, 110K, and 111K. The resistors are guaranteed accurate within 0.1% of their stated values, but the actual value as measured by our HP 3458A (.001% accuracy on OHMS) is recorded on the circuit board adjacent to the resistors.
Set your DMM to measure DC current and connect your test leads to the provided terminals. A precise 1.000mA will flow through your meter.
Thanks for looking, and to my fellow Amateur Radio Operators, 73
