Low cost Voltage References
              Malone Electronics                     
www.voltagestandard.com
418 W. Main St. #1542
Battle Ground, WA 98604 USA
email: doug@voltagestandard.com
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                                                                                                                                                       DMMCheck
                                                                                                       

            

The DMMCheck is a battery powered device that checks three important functions on a DMM - DC Volts, Resistance and DC current.  It you have a DVM or DMM that is several years old, the DMMCheck can provide you with the confidence you need to know if you can trust your test equipment.

Provided on the small (3" x 3") circuit board are three separate circuits:
1.  A 5VDC voltage reference (based on Linear Technology LTC1021BCN8-5) that is accurate to within 0.007% (plus or minus 350uV) for a minimum of 6 months.
2.  A 1.000mA DC active current source that is accurate to within 0.1% (plus or minus 1uA)
3.  Three 0.1%, 25ppm/C resistors  (Yageo MFP series)- 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.


5VDC VOLTAGE REFERENCE:

After the DMMCheck is assembled, it is powered up with a 9V power supply for a minimum of 250 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 Keysight 3458A  DMM that has an accuracy of 0.0008% (Keysight Technologies, Loveland Standards and Calibration Labs, Certificate of Calibration 1-7581424013-1, valid through Jan 21, 2017).  Accidental movement of the trimpot adjustment is prevented by the application of a small amount of acrylic enamel.  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.

Recalibration of the voltage reference is free for the first two years after purchase - just send it back to us and include $4.00 in stamps for return shipping within USA.  After two years the charge is $10.00 plus shipping. Please contact us for shipping charges to destinations outside the USA.


PRECISION RESISTORS:

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 obtained with a 4-wire (Kelvin) measurement using our HP 3458A (.001% accuracy on OHMS) is recorded on the circuit board adjacent to the resistors.

Optional, extremely stable (Vishay type PTF56, 10ppm) resistors are available for an additional $4.00 - please specify on your order if you would like this option installed.

1.000mA DC CURRENT SOURCE

A 0.1% accurate active 1mA DC current source is provided to check the DC current measurement accuracy of your DMM.  The compliance voltage is approximately 2V and accommodates resistances between 0Ohms and 2KOhms.To use this feature, set your DMM to measure DC current and connect the test leads to the provided current source terminals.  The DC current sourced by DMMCheck is guaranteed to be within 0.999mA and 1.001mA, with the actual value, as measured by our 3458A, indicated on the included instruction/data sheet.




Optional Enclosure
The DMMCheck optional enclosure (shown above) provides the following:
• Same circuitry and electrical specifications as the standard DMMCheck

• Black plastic enclosure surrounds 9V battery mounted underneath circuit board
• Small rubber feet in bottom corners of enclosure keep unit from sliding on your work surface
• Clear 1/8" thick acrylic cover plate prevents damage if an object is accidentally dropped onto your DMMCheck.  Since the cover is clear, the power-on LED and connection terminals are easily seen.


Dimensions (no enclosure): 3" W x 3" L x 1.25" H
Dimensions (with enclosure option): 3" W x 3" L x 2 1/8" H


Here is an example of the measured-value record that is included with every DMMCheck:





Shown below is our 3458A in 4-wire (Kelvin) resistance mode measuring a DMMCheck 100K OHM precision resistor.