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 pictures, 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. Black
plastic enclosure surrounds 9V batteries mounted underneath circuit
board. Small rubber feet in bottom enclosure corners help keep unit
from sliding on your work surface. Clear 1/8" thick acrylic cover plate
prevents damage if an object is accidentally dropped onto the unit.
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. 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 Calibration Labs, Certificate 1-7581424013-1, valid through January 21, 2017). 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-
please specify on your order if you need a cal outside standard 68-70 F
range at no extra charge. A "Measured Values" certificate is included as shown in the third listing photo. The last listing photo shows stability over a 8 month period for one of our test units. Day to day variations are due to ambient temperature changes. The gap in data at around the 5000-hour mark is when our 3458A went out for calibration.
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 circuit board and the
- supply output connects to the - terminal of Batt 2. As shown in the
listing photos, 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 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
several minutes before use; typical settling time is about 2 minutes as
shown in the second listing photo.
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 to USA 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.
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 worst-case
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