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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VREF10-003, Precision DC Voltage Reference
This small, portable, precision voltage reference can be
used to check the calibration of your DVM or DMM. The VREF10 features a
10.00000V output, and is conservatively rated to be accurate within
0.003% for a minimum of 6 months. The circuit is based on the Linear
Technology LT1021BCN8-10 which uses buried Zener technology resulting in
excellent long term stability. Here is a link to the LT1021 datasheet
on the Linear Technology website: http://cds.linear.com/docs/en/datasheet/1021fc.pdf
As shown in the above picture, the circuit board was designed to minimize the effects of mechanical stress on the reference IC. Specifically, the LT1021 is placed on the edge of the board and 2 adjacent slots decouple stresses in the board from reaching the reference which could otherwise cause the output voltage to shift.
Having designed and built battery powered DC voltage references for over seven years, we have acquired the skill to carefully and quickly solder the reference IC to the board without degrading its performance.
An external power supply is not needed. Two Alkaline 9V batteries are included which makes the unit completely self contained and easily transported. An on-board on/off switch allows you to maximize battery life when not in use. Current drain is less than 5mA so the batteries will last many 10's of hours. An on board voltage regulator supplies a constant input voltage to the LT1021 as the batteries slowly decrease to their replacement voltage of 7V. Reverse polarity protection is included, so even if one or both batteries is placed in their holder backwards, no damage will result. A high brightness, low current LED clearly indicates when the unit is powered on.
After the unit is assembled, it is powered up with an 18V power supply for a minimum of 1000 hours to "age" the reference and confirm its long term stability. During this aging process, daily measurements are made of the reference output voltage- the LT1021 is replaced on those units that have excessive long term drift or temperature coefficient. After aging, a trim potentiometer is carefully adjusted so that the output voltage is within 5uv of 10.000000V as measured by our calibrated, 8.5 digit Keysight 3458A DMM. (Keysight technologies, Certificate of Calibration 1-8526526825-1, valid through January 31, 2018). The ambient temperature is recorded and unless specified otherwise will be in the range 68 to 70 degrees F. We can perform calibration at temperatures between 65 and 80 degrees F- please specify on your order if you need a no extra charge cal outside the standard 68-70 F range.
If desired, the VREF10 can be powered by an external DC power supply instead of using the included batteries. It is recommended that a linear (as opposed to switching) supply be used and all VREF10 specifications are met as long as the external supply voltage is between 14V and 19V. If an external power supply is used, the supplied batteries should be removed from their holders and the + supply output connects to the + terminal of Batt 1 on the VREF10-003 circuit board and the - supply output connects to the - terminal of Batt 2. As shown in the above photo, the 9V battery holder terminals stick up through the circuit board and can be used as the tie points for an external supply or the connection point for a DMM to measure the battery voltage.
There are two distinct advantages to the VREF10 being battery powered. First, there is no possibility of power supply noise/ripple from getting onto the reference output. Second, since the battery power supply for the VREF10-003 is completely isolated from ground and any circuit connections you may make, multiple units can be can be connected in series to generate 20V, 30V or more.
As shown in the above picture, the circuit board was designed to minimize the effects of mechanical stress on the reference IC. Specifically, the LT1021 is placed on the edge of the board and 2 adjacent slots decouple stresses in the board from reaching the reference which could otherwise cause the output voltage to shift.
Having designed and built battery powered DC voltage references for over seven years, we have acquired the skill to carefully and quickly solder the reference IC to the board without degrading its performance.
An external power supply is not needed. Two Alkaline 9V batteries are included which makes the unit completely self contained and easily transported. An on-board on/off switch allows you to maximize battery life when not in use. Current drain is less than 5mA so the batteries will last many 10's of hours. An on board voltage regulator supplies a constant input voltage to the LT1021 as the batteries slowly decrease to their replacement voltage of 7V. Reverse polarity protection is included, so even if one or both batteries is placed in their holder backwards, no damage will result. A high brightness, low current LED clearly indicates when the unit is powered on.
After the unit is assembled, it is powered up with an 18V power supply for a minimum of 1000 hours to "age" the reference and confirm its long term stability. During this aging process, daily measurements are made of the reference output voltage- the LT1021 is replaced on those units that have excessive long term drift or temperature coefficient. After aging, a trim potentiometer is carefully adjusted so that the output voltage is within 5uv of 10.000000V as measured by our calibrated, 8.5 digit Keysight 3458A DMM. (Keysight technologies, Certificate of Calibration 1-8526526825-1, valid through January 31, 2018). The ambient temperature is recorded and unless specified otherwise will be in the range 68 to 70 degrees F. We can perform calibration at temperatures between 65 and 80 degrees F- please specify on your order if you need a no extra charge cal outside the standard 68-70 F range.
If desired, the VREF10 can be powered by an external DC power supply instead of using the included batteries. It is recommended that a linear (as opposed to switching) supply be used and all VREF10 specifications are met as long as the external supply voltage is between 14V and 19V. If an external power supply is used, the supplied batteries should be removed from their holders and the + supply output connects to the + terminal of Batt 1 on the VREF10-003 circuit board and the - supply output connects to the - terminal of Batt 2. As shown in the above photo, the 9V battery holder terminals stick up through the circuit board and can be used as the tie points for an external supply or the connection point for a DMM to measure the battery voltage.
There are two distinct advantages to the VREF10 being battery powered. First, there is no possibility of power supply noise/ripple from getting onto the reference output. Second, since the battery power supply for the VREF10-003 is completely isolated from ground and any circuit connections you may make, multiple units can be can be connected in series to generate 20V, 30V or more.
For
maximum accuracy it is recommended that the reference be powered-up 15 minutes before use.
As a benefit to our customers, and to keep the cost of ownership as low as possible, recalibration is free for the first two years after purchase- just send it back to us and for USPS Priority return shipping please include $7.00 in stamps or US currency or PayPal payment to doug@voltagestandard.com. After two years the calibration charge is $10.00 plus shipping. Please inquire for shipping charges to destinations outside the USA.
Here is an example of the Measured Value record that is included with every Vref10-003:
Vref10-003 optional enclosure (shown below) provides the following:
• Same circuitry and electrical specifications as the standard Vref10
• Black plastic enclosure surrounds the 9V batteries 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 Vref10. Since the cover is clear, the power-on LED and connection terminals are easily seen.
• Robust PCB turret output terminals for connection to your DMM
Specification Summary:
Voltage reference IC: Linear Technology LT1021BCN8-10
6 month output voltage accuracy: 0.003%
Output voltage temperature coefficient: 1.4ppm/C typical, 2.5ppm/C maximum
Maximum output load current: 10mA; LT1021 has short circuit protection
Load regulation: 20ppm/mA max, 10ppm/mA typ
Power source: two Alkaline 9V batteries (supplied)
Current drain: less than 5mA
Dimensions: 3"W x 3"L x 2.1"H
Designed, assembled, and calibrated in the USA
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