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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VREF10-002, Precision DC Voltage Reference
10-16-2019 Update: Our thermal chamber is finally up and running again and we can accept and ship orders again. Thank you for your patience.
Recent Improvements:
1. Guaranteed accuracy is now 0.0025%
2. The On/Off switch is now right-angle which makes it easier to access the switch toggle, especially when the optional enclosure/cover plate is ordered.
3. The LT1021 Reference IC now has a conformal coating applied to minimize the effects of humidity.
4. The guaranteed Temperature Coefficient has been reduced to ±5µV/°F (±0.9ppm/C) typical, ±7µV/°F (±1.3ppm/C) maximum.
5. All units are temperature tested in our thermal chamber. Over an 8-hour period the temperature is gradually increased from 60°F to 90°F while the Reference voltage output is measured with our Keysight 34972A Data Acquistion system. A graph of Reference voltage versus temperature is produced (see below for an example) from which the temperature coefficient (TC) can be determined. If the TC is greater than ±7µV/°F (±1.4ppm/C) then temperature compensation components are added and the temperature cycle is repeated to confirm the resulting improvement in TC. The temperature graph for your particular VREF10-002 is available as an option via our online store.
This small, portable, precision voltage reference can be
used to check the calibration of your DVM or DMM. The VREF10-002 features a
10.00000V output, and is conservatively rated to be accurate within
0.0025% 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 eight 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.. 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, Loveland Standards Laboratory Certificate of Calibration 1-10871332528-1, valid
through February 27, 2020). The ambient temperature is recorded and
unless specified otherwise will be in the range 68 to 70 degrees F. We
can perform calibration at other temperatures- please inquire for feasibility and pricing/
If desired, the VREF10-002 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 VREF10-002 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 VREF10-002 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 VREF10-002 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 VREF10-002 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.
Recalibration is free for the first two years after purchase-
just mail it back to us and for USPS Priority return shipping to destinations within the USA please send a $8.00 PayPal payment to doug@voltagestandard.com. After two years the calibration charge is $10.00 plus shipping.
Here is an example of the Measured Value record that is included with every Vref10-002:
Here is an example of Reference output voltage as the temperature in our thermal chamber changes from 60°F to 90° over a period of 8 hours:
Vref10-002 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 (60°F- 90°F): ±5µV/°F (±0.9ppm/C ) typ, ±7µV/°F (±1.3ppm/C) max Maximum output load current: 10mA; LT1021 has short circuit protection Load regulation: 10ppm/mA typical, 20ppm/mA maximum Power source: two Alkaline 9V batteries (supplied) Current drain: less than 5mA Dimensions: 3"W x 3"L x 2.1"H