Simple Voltage Reference Project - Page 1
Forum section: electronics / projects

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 06:01:56 am
content: Hello!I recently noticed I have 3x REF02 5v precision voltage reference IC's.I am wondering if I can use one to make an accurate 5v reference to calibrate DMM's with.I also saw a circuit in the data sheet for the REF02 that said the chip could be used to make a constant current supply and I wanted to know if I could do that easily and use it to calibrate DMM's.ThanksEDIT:Here it is currently (I need more solder to completely finish it but here it is)

author: Lightages
author_rank: Unknown
timestamp: July 31, 2013, 06:58:18 am
content: The REF02 is a low precision voltage reference. Yes you can make a simple circuit and have a reference within 0.3%. This would be good as a sanity check on a multimeter to see that it is reading OK. You would not be able calibrate any better than to maybe 1% with confidence. You really should have a reference that is an order of magnitude better than what you are trying to calibrate to.The other consideration is if your multimeter has simple trim pots to make the adjustment or if it is software based. With a trim pot based one you just need to tweak the pot until you get the correct reading on the meter. With software based adjusting meters you rarely find then wanting to see a 5V input as their reference. Usually they will want multiples of voltages live 1.9V or 3.5V for example.Why not build a couple circuits anyway. It will be very simple and they can run from a 9V battery very well.http://www.ti.com/lit/ds/sbvs003b/sbvs003b.pdf

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 04:13:35 pm
content: Quote from: Lightages on July 31, 2013, 06:58:18 amSounds like a good idea to make one and use it as the sanity check.I might actually use it to calibrate my current DMM because this DMM only claims like 1% accuracy. I think most of the DMM's I might buy in the future will probably all be manual calibration (older flukes) so we should be good there.I have a question though, how clean does the power coming into this chip need to be? I guess if it needs to be really clean I will just use a 9v battery but I did also want to put a little DC power jack on it (I have 3 laying around) that correspond to some 9v 1a wall warts I have.Also, do you know any high precision voltage reference IC's that you know off hand that would be precise enough to calibrate old flukes but have a simple circuit?Thanks for your help.

author: Unknown
author_rank: Unknown
timestamp: July 31, 2013, 04:51:53 pm
content: For real calibration, you will need multiple voltages ranging from say 100 mV to 1000 V. Also AC voltages up to 600 V at several frequencies and standard resistors. Read through the performance verification or adjustment section of a Fluke service manual to get an idea what's involved. The old Fluke 87(-I), for example, requires DC voltages from 0 V to 1 kV at 0.035% accuracy, AC voltages from 0V to 1kV at 60 Hz to 20 kHz at ~0.2% accuracy, currents up to 10 A both DC and AC up to 1 kHz and resistors between 1 Ohm and 100 Mohm with ~0.06% accuracy. Unless you have a small cal lab at home (there are some people guilty of this on this forum), leaving the meter alone unless it's obviously out of spec is usually the best strategy. Themini metrology labseries by Conrad Hoffman could give you an impression what's involved to derive multiple voltages from a single reference. But that would be limited to DC voltages.If you just want to do a spot check, the voltage references sold byVoltagestandardandGeller Labsare a good choice. The advantage you get from buying a pre-made reference is that someone will have calibrated it with a high-precision DMM with traceable calibration to a much higher accuracy than offered by the IC manufacturer. The Voltagestandard DMMCheck (plus) would probably be suitable. But note this is only for checks: it's not sufficient for calibrating a serious DMM.If you want to go the DIY route, thenthis threadmight be of interest. There are at least half a dozen other threads about voltage references on this forum (Google is quite good at searching eevblog.com), but the general trend is to try to make a stable reference and then use a DMM to figure out the value, as opposed to trying to buy an IC with a very good initial accuracy.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 05:01:14 pm
content: Quote from: alm on July 31, 2013, 04:51:53 pmWell I don't really think it'd be nessary to go to those extremes. I mean if I buy a fluke and its seirously out of wack, I just want something that will get it back into acceptable range again. Theres no way I'll ever pay to have a DMM calibrated so whatever I can do at home is the best any of my DMM's will ever see.I am still wondering how clean the DC needs to be that I'm feeding the REF02. Does it need to be clean at all, very clean, or can it be straight off a bridge rectifier?

author: c4757p
author_rank: Super Contributor
timestamp: July 31, 2013, 05:06:58 pm
content: Regulated with an LM317 should be more than enough for this level of accuracy.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 05:09:15 pm
content: Quote from: c4757p on July 31, 2013, 05:06:58 pmWait do you mean use that as in input for my REF02 or are you saying I don't need the REF02?

author: c4757p
author_rank: Super Contributor
timestamp: July 31, 2013, 05:11:39 pm
content: As the input to the REF02. LM317 can't even calibrate an old analog meter...

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 05:14:11 pm
content: Quote from: c4757p on July 31, 2013, 05:11:39 pmOkay that's what I thought but I was just making sure.Well how would it do running off of just a 9v battery? I don't have any lm317's on hand and I don't want to get one just so I can use a wall wart on this if a battery will do fine.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 07:57:45 pm
content: I'm still waiting on whether a 9v battery is good enough before I solder this up......

author: Lightages
author_rank: Unknown
timestamp: July 31, 2013, 08:07:59 pm
content: I mentioned right at the beginning that a 9V battery would be fine. All the information you need is in that data sheet I linked too.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 08:14:08 pm
content: Quote from: Lightages on July 31, 2013, 08:07:59 pmWell the data sheet doesn't specifically say how clean the power needs to be.I'll go solder this up.

author: c4757p
author_rank: Super Contributor
timestamp: July 31, 2013, 08:15:42 pm
content: Yes it does, it's right on the front page in the marketing blurb:Quote

author: AG6QR
author_rank: Frequent Contributor
timestamp: July 31, 2013, 08:24:56 pm
content: Quote from: EpicIntelGamer on July 31, 2013, 08:14:08 pmIt does, indirectly. Unless you specify exactly how much output noise you could tolerate, it won't tell exactly how much supply noise you'll be able to tolerate. But the "Typical performance curves" on page 4 tell you how noise on the supply voltage may be transferred to the output. See in particular the "Line regulation vs. Frequency" graph and the "Line regulation vs Supply voltage" graphs.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 08:26:36 pm
content: Quote from: c4757p on July 31, 2013, 08:15:42 pmThat's the output, no?

author: Lightages
author_rank: Unknown
timestamp: July 31, 2013, 09:15:02 pm
content: That tells you how much the output changes based on the input voltage. The 9V battery will be fine. Just change it when it gets down to 8V.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 09:25:02 pm
content: Quote from: Lightages on July 31, 2013, 09:15:02 pmWhy change it at 8, it runs down to 7v......

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 09:28:59 pm
content: Here's the finished product!Well almost finished, I ran out of solder and was unable to finish the positive pad and also unable to make the negative pad.I decided to make another way for the DMM to connect to the board besides banana jacks (I didn't want to use any of my remaining precious binding posts) so I thought I'd make pads on the underside of the edge of the board where I could clip on alligator clips connected to the DMM!Here is how it looks!

author: Lightages
author_rank: Unknown
timestamp: July 31, 2013, 09:45:52 pm
content: Quote from: EpicIntelGamer on July 31, 2013, 09:25:02 pmYes it will run down to 7 volts but you try to avoid the extremes of the operation limits of devicesAnother hint. If you are going to make another one it is better to not solder the chip to the board. It would be better to use a good IC socket instead. Soldering directly to the board introduces unnecessary thermal stress and physical stress to the chip. With the REF02 this is probably not a big deal but it is general practice to stress reference chips the least you can.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 09:50:58 pm
content: Quote from: Lightages on July 31, 2013, 09:45:52 pmI actually have some 8pin sockets but I was too lazy to de-solder them from what they are on.I completely understand the thermal stress but what do you mean physical stress?

author: Lightages
author_rank: Unknown
timestamp: July 31, 2013, 09:55:38 pm
content: After you solder a device to the circuit board things cool down and the differential expansion of the materials cause physical stresses. Changes in ambient temperature can cause differential expansion and contraction of the different materials which then cause changing stresses and that can cause more drift.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: July 31, 2013, 10:59:50 pm
content: Quote from: Lightages on July 31, 2013, 09:55:38 pmWow that's actually good to know.I really thought sockets were only used for ease of replacements of the parts.Thanks for the info!

author: PA4TIM
author_rank: Super Contributor
timestamp: July 31, 2013, 11:51:20 pm
content: I do it this way. these are the opamps following a LM399. But the 399 is mounted the same way.By the way, a friend made a reference with a 7805 and a LM317, just for fun, he got it very stable. So do not say you can not even calibrate an analog meter with it (besides that, I have an analog meter that can do 1uV full scale ;-) )By the way, this LM317 was build using shielding, ovenized, good connections to the meter etc but his first test with a standard non shielded but well build 7805 and LM317 based reference drifted also less as 500 uVThe reference , building it right and good components all are important. I made very good references with 4 cheap TL431 parallel.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 01, 2013, 12:55:12 am
content: Quote from: PA4TIM on July 31, 2013, 11:51:20 pmAre those the things from single inline headers?That's pretty cool what your friend did!How good is your quad TL431 reference? Is it good enough to use to calibrate DMM's?

author: c4757p
author_rank: Super Contributor
timestamp: August 01, 2013, 12:57:45 am
content: Quote from: EpicIntelGamer on August 01, 2013, 12:55:12 amIndeed it does.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 01, 2013, 12:59:53 am
content: Quote from: c4757p on August 01, 2013, 12:57:45 amOh I guess I posted this in the wrong threadThat was meant to go in my Homemade PSU V2 Thread lol

author: PA4TIM
author_rank: Super Contributor
timestamp: August 01, 2013, 06:51:38 am
content: No, they are not from headers ( those do not have the golden inner "springs" ) but from a pcb out of some medical instrument. But you can use the pins from a good IC socket too.Every Vref is usefull to calibrate something as long as it's value is much better known as that somethings accuracy.You can build something with 4 TL431 like I did, it makes 10V but without reference or calibration you will never know the value.A reference itself had several things. It has a typical value. Most can en will deviade a few mV from that. They most times come in several grades. The more change it is close to typical, the more expensive. The LT1027 for instance is in a A,B and C grade. The A grade is very hard to find, most sell the C grade, LT only samples the B, the A is the best.So that makes a TL431 ( or other simple reference) without calibration only usefull for a cheap 2,5 digit multimeter or AVO 8 or so.A reference needs time to stabilize. The fist few hunderd hours they change the mostThe change by temp, relative humidity etc, but that is in the tens/hundereds of uV region. Not important for a 3,5 digit 1% meter.Most references do not like o be loaded direct by a meter, they need a buffer amp behind them.I have 7,5 digit meters, calibrators and standards so I can adjust and monitor a Vref with some confidence. Problem is the climate change in my lab. This gives me a 100 uV uncertanty. I have a climate independed knowh source so with a lot of work and enough speed I can bring it down to less as 5 uV

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 21, 2013, 05:03:13 pm
content: Been a while since there was activity in my thread and I recently thought of something and figured I'd ask here.Now that I have a pretty nice reference (It shows 5.009VDC on my most accurate 4.5Digit meter which was last calibrated in 2004), is there a way I can use it or perhaps another REF02 regulator to help make a reasonably accurate current source?

author: ve7xen
author_rank: Super Contributor
timestamp: August 22, 2013, 05:22:00 pm
content: Quote from: EpicIntelGamer on August 21, 2013, 05:03:13 pmThere are many ways, of course. A low offset opamp and a circuit like one of these:http://www.maximintegrated.com/app-notes/index.mvp/id/3869with a precision resistor will get you reasonable accuracy for a low current source (e.g. 1mA).