# 2.048v Voltage Reference..

#### DickCappels

Joined Aug 21, 2008
10,246
I just ordered a 2.5V/ 5V/ 7.5V/ 10V voltage reference from one of those mysterious vendors based in Hong Kong. It is based on the AD584 and is offered at less than US$4 including shipping. Its outputs are to be measured on a presumably calibrated six digit Agilent meter and recorded. It should be interesting to test. http://www.ebay.com/itm/131740362946 There are others offered on eBay, apparently from different suppliers. The problem of getting an output below 2 volts can be solved with a precision voltage divider. Example: Make a 2:1 divider, connect it to a power supply, and measure the output (maybe be measured against a reference voltage so a low scale can be used to increase resolution). Note the reading and then swap the two resistors. Change one resistor and try again until you have an acceptably small difference when swapping resistors or you run out of new resistors. #### MrAl Joined Jun 17, 2014 11,715 I just ordered a 2.5V/ 5V/ 7.5V/ 10V voltage reference from one of those mysterious vendors based in Hong Kong. It is based on the AD584 and is offered at less than US$4 including shipping. Its outputs are to be measured on a presumably calibrated six digit Agilent meter and recorded.

It should be interesting to test.
http://www.ebay.com/itm/131740362946

There are others offered on eBay, apparently from different suppliers.

The problem of getting an output below 2 volts can be solved with a precision voltage divider.

Example:
Make a 2:1 divider, connect it to a power supply, and measure the output (maybe be measured against a reference voltage so a low scale can be used to increase resolution). Note the reading and then swap the two resistors. Change one resistor and try again until you have an acceptably small difference when swapping resistors or you run out of new resistors.
Hi,

You beat me to it

I was going to mention that trick but with a little twist...

If the higher value resistor is paralleled with another high value, we can then swap again to check, and keep doing that until we get the accepted readings.

Also, we can do this with a 3:1 divider using the same idea, but using three resistors and more swapping.

The main problem is that most meters go to either 1.999 or 3.999, and 2.048 is a little too high for the 1.999 meters so we would like to divide down to get a better value for reading on the 1.999 meters. Using the 3:1 method we could get closer enough to 1.999v which would be about 1.365 volts by measuring across the two lower resistors. I might be satisfied with that myself, otherwise maybe go to a 4:1 divider which would take longer to make i think.

#### Dr.killjoy

Joined Apr 28, 2013
1,196
Sorry about the no updates as work has been getting busy and I am still working on the Tek 2215 scope ..

@DickCappels or anyone
You mentions a 2:1 voltage divider but couldn't I just use a simple voltage with .01% or better resistor with both resistors being 50K ohm or 5K ohms for a 1.024V output??? Sorry about the different ohms as I wasn't sure how to figure out whether 50k ohm or 5k ohm would be best.. I was just going to to make a test circuit and see what the out come would be but would like some input if you can ..

#### MrChips

Joined Oct 2, 2009
31,083
You don't want to use 50kΩ resistors because you are forgetting the fact that your test meter has resistance as well.
If your DVM has an internal resistance of 10MΩ which is typical, you will get 1.021V reading on the display, not 1.024V.

If you use a voltage divider with 100Ω and 3900Ω you will get 1.9968V output.
With a 10MΩ meter, this will drop to 1.996781V, assuming your resistors are better than 0.001% tolerance.

#### Dr.killjoy

Joined Apr 28, 2013
1,196
You don't want to use 50kΩ resistors because you are forgetting the fact that your test meter has resistance as well.
If your DVM has an internal resistance of 10MΩ which is typical, you will get 1.021V reading on the display, not 1.024V.

If you use a voltage divider with 100Ω and 3900Ω you will get 1.9968V output.
With a 10MΩ meter, this will drop to 1.996781V, assuming your resistors are better than 0.001% tolerance.
I forgot about that and thanks for reminding me. The voltage divider is not set in stone but will continue when the other part of the circuit is done and running correctly

Hello,

With a REF102 and an INA105 or OPA277, you can create a adjustable reference.
See the attached application note.

If you want a pure 2.048 voltage reference, look for the ADR4520:

Bertus
That article was really cool and thank you very much.. My plan was to use just a simply 2.048v Ref chip and the chip you mentioned is better in specs but almost double in price compared to Maxiam chip.. But I will have to do some research to find a better chip with maybe a better price too ..

#### Lestraveled

Joined May 19, 2014
1,946
@Dr.killjoy
Buy an HP 3478A multimeter. They are cheap and extremely accurate. They are also the cheapest meter to have calibrated. Buying a used HP3478A will probably be more accurate then chasing a voltage reference chip.

I have three HP3478A meters. One is calibrated and I use it to verify the others.

#### DickCappels

Joined Aug 21, 2008
10,246

#### Lestraveled

Joined May 19, 2014
1,946
@DickCappels
Well, I was into repairing test equipment and was always trolling EBay for good deals, and ..........I..........just ............can't...............resist.........a.....good...........deal.

But I'm better now.