Guaranteed accuracy, for a minimum of 8 months, is now 0.0025%
The On/Off switch is now right-angle which makes it easier to access the switch toggle, especially when the optional enclosure/coverplate option is ordered.
The LT1021 Reference IC now has conformal coating applied to minimize the effects of humidity.
The guaranteed Temperature Coefficient has been reduced to ±5µV/°F (±0.9ppm/C) typical, ±7µV/°F (±1.3ppm/C) maximum.
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 10.0000V output, and is conservatively rated to be accurate within 0.0025% for a minimum of 8 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.
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 2000 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 pot 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.
The VREF10-002 optional enclosure (shown below) provides the following:
• Same circuitry and electrical specifications as the basic VREF10-002 PCB
• Black plastic enclosure surrounds 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 VREF10-002. Since the cover is clear, the power-on LED, on/off switch, and connection terminals are easily seen and accessed.
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 $8.25 PayPal payment to firstname.lastname@example.org. After two years the calibration charge is $10.00 plus shipping. Link to our online store: www.shop.voltagestandard.com