Calibration of an ANENG AN870 - Page 1
Forum section: electronics / testgear

author: fant
author_rank: Contributor
timestamp: October 24, 2020, 02:26:59 pm
content: Good morning;anybody knows how to calibrate the ANENG AN870?I have the multimeter that with a DC input voltage of 10,00000 V, read 10,008 V and I would like to calibrate it.Thank you in advance

author: ebclr
author_rank: Super Contributor
timestamp: October 24, 2020, 03:26:05 pm
content: Are you kidding?

author: radiolistener
author_rank: Super Contributor
timestamp: October 24, 2020, 04:16:57 pm
content: Quote from: fant on October 24, 2020, 02:26:59 pmtry to put it near the heater or piece of ice

author: Fungus
author_rank: Super Contributor
timestamp: October 24, 2020, 05:11:35 pm
content: Quote from: fant on October 24, 2020, 02:26:59 pmTry cooling it down a bit.(Seriously: Put it in the fridge for an hour then measure again...see the problem?)

author: MiroS
author_rank: Regular Contributor
timestamp: October 24, 2020, 05:42:34 pm
content: Quote from: Fungus on October 24, 2020, 05:11:35 pm... or put sticker on LCD 10,00000 VIt will be rock solid.

author: floobydust
author_rank: Super Contributor
timestamp: October 24, 2020, 08:09:45 pm
content: OP I think you are 0.08% out on one range of a 0.05%+3sd spec'd multimeterIf you did calibrate it perfectly, that is not long-term accuracy because it uses vanilla 1% tolerance resistors and an ICL8069, both of which will drift with temperature and age.It is not easy calibrating an ANENG multimeter. With older builds, the cal co-efficients are stored in EEPROM with a Write-protect.You have to take the meter apart and jumper the write-protect, put it in cal mode. The known procedure ishorribly translated from chineseand might not even apply exactly to the AN870 firmware. Otherwise, you have to hack the EEPROM. Newer multimeter pcb builds have no external EEPROM and I have not looked into how calibration is done there.https://www.eevblog.com/forum/testgear/cheap-aneng-meter-calibrationreset-procedure/msg1969907/#msg1969907

author: fant
author_rank: Contributor
timestamp: October 24, 2020, 09:24:49 pm
content: Thank you for the answer, floobydust.I know that such multimeters are not HP, but I want to try anyway.BTW, this is my calibrated reference, and this is HP.

author: Fungus
author_rank: Super Contributor
timestamp: October 25, 2020, 06:15:26 am
content: Those bench meters have an internal heater and thermostat for their critical components.

author: fant
author_rank: Contributor
timestamp: October 25, 2020, 04:37:11 pm
content: I think to know how they are made, having three 3458 in the lab ( one of them, the one on the picture, powered 24/7 ).My request was on how to calibrate the unit, then if it is close, far or completely out of order it is my problem.And only one guy (that I thanks) helped me, the others just used bits to move air.Best regards

author: bdunham7
author_rank: Super Contributor
timestamp: October 25, 2020, 05:45:06 pm
content: Quote from: fant on October 25, 2020, 04:37:11 pmFor someone with 3 HP3478s, you are asking a rather imprecise question.You appear to be actually asking "how do I change the gain constants in the calibration memory" or perhaps "what is the manufacturer's calibration procedure", the second of which might be a better question if it weren't for the fact the the product is an unsupported basement-bargain POS. In either case, user floobydust apparently has some experience or knowledge and it looks like it would be a challenge, given the complete lack of support that you generally find for this level of product.However, if you are motivated by anything other than idle curiosity as to how to enter new gain constants and you actually care whether the meter is accurate or not, you would want additional data, such as what does it read at 5.00000 V and 15.00000V? You certainly have the means to check that. And even if you only want to measure 10 volts for some reason, how consistent is that 10.0008V and under what conditions? Absent a specific manufacturer procedure, unless you take the time to characterize the meter for linearity, tempco and stability you aren't 'calibrating' anything, you are just doing the modern version of twiddling the knobs without a plan.

author: fant
author_rank: Contributor
timestamp: October 25, 2020, 06:01:51 pm
content: Good morning;I use all the meters in the lab, temperature from 20 to 23 °C, look here:https://www.eevblog.com/forum/metrology/vintage-weston-element-is-it-any-good/msg3101976/#msg3101976,first picture.Sorry if I have forgotten the words "calibration memory" but, if a person has already done the work, knows that there is an EEPROM inside.Anyway, this is the workhorse we have (actually 5 units) in the lab and all are with a reading little bigger than the correct one.For this reason I wanted to test on one of them the possibility to correct the reading.For the official use in front of the customers we use the Agilent 34401 that is periodically calibrated by an external company.best regards

author: 2N3055
author_rank: Super Contributor
timestamp: October 25, 2020, 06:25:46 pm
content: Quote from: fant on October 25, 2020, 04:37:11 pmLOL.No, other didn't just move air. They went out of their way to politely explain you that your question is, well, nonsense.. Nad wanted to save you grief of lost time for no particular result.It makes no sense to adjust that very cheap instrument to be better than 500 ppm accuracy. Because it is not stable enough to keep that across even few °C around 23°C. It will also drift with humidity changes and generally drift because of components used.It is a miracle that they are as accurate and stable as they are..They merely wanted to point out it is not useful to do so.. If you want to do it for fun, without expectations that 2 weeks later it will hold adjustment, then by all means..

author: bdunham7
author_rank: Super Contributor
timestamp: October 25, 2020, 07:11:03 pm
content: Quote from: fant on October 25, 2020, 06:01:51 pmFascinating that you have not one, but three reference meters that I can't possibly justify even one of, but your everyday 'workhorse' , in a use where precision appears to matter, literally costs less than my test leads. You have to understand that many will find that difficult to understand!So, as for getting your meters to read accurately, is the high reading consistent over time and scale? Do you get10.000810.008 volts from all of them every time you try? If not, how much variance? And how about 5.00000 and 15.00000? Is it 5.004 and 15.012? If not, what is changing the gain constant really going to get you? If so, and assuming you don't solve the issue of changing the calibration memory, perhaps you could simply try adding 8K resistance to the test leads and see if the results are acceptable. If so, find the 10M input resistor and add 8K to it. Or, remove and measure it and sub in a low-tempco resistor with about 8K more resistance. From another thread, I think that the 10M input is R29 + R30, but I'm not at all sure since I don't have an example here.

author: fant
author_rank: Contributor
timestamp: October 25, 2020, 11:27:02 pm
content: Nothing fascinating.On the normal work, when you have to see the voltage of a power supply, you use the 870, when you have to see the reference for a 18 bit A/D converter to read altitude you use the 3458.And during the test with customers only 34401 are allowed.Anyway, the discussion is not going in the direction to solve the problem and for me is closed.Best regards

author: coromonadalix
author_rank: Super Contributor
timestamp: October 26, 2020, 12:51:51 am
content: something like this ?https://www.eevblog.com/forum/testgear/cheap-aneng-meter-calibrationreset-procedure/http://www.kerrywong.com/2016/03/19/hacking-dtm0660l-based-multimeters/https://www.eevblog.com/forum/testgear/the-official-an8008-meterthread/youll have to sniff the eeprom and decypher it to get the cal constants or use some of the links methods ??

author: Fungus
author_rank: Super Contributor
timestamp: October 26, 2020, 05:29:05 am
content: Quote from: fant on October 25, 2020, 04:37:11 pmMoving air is the real problem. Even if you calibrate it it might be wrong in a few hours because the sun changed position and temperature changed by one degree.So... before you even attempt to adjust this meter, it's a good idea to find out how much it's affected by temperature. ie. put it in the fridge for a while. Put it in a warm place for a while. See how much it changes.After that you'll need to find a small EEPROM inside it that holds calibration data for each range and figure out how to read/modify it.

author: Trader
author_rank: Frequent Contributor
timestamp: July 12, 2021, 07:50:39 pm
content: Sorry about my naive question, I know the way to calibrate those DMMs is through the EEPROM, but since they use the ICL8069 voltage reference, why not discover that resistor responsible to the output voltage and just adjust it?https://datasheets.maximintegrated.com/en/ds/ICL8069.pdf

author: Fungus
author_rank: Super Contributor
timestamp: July 12, 2021, 07:53:29 pm
content: Quote from: Trader on July 12, 2021, 07:50:39 pmSimple: Because each range has a separate calibration. If you change that then you makeeverythingchange.Plus: I don't think there's a potentiometer. The reference is set approximately then everything else is done in software.

author: Trader
author_rank: Frequent Contributor
timestamp: July 12, 2021, 10:58:47 pm
content: Quote from: Fungus on July 12, 2021, 07:53:29 pmQuote from: floobydust on October 24, 2020, 08:09:45 pmI thought the DMM lost the calibration because of the ICL8069 and the adjust-resistor. So, fixing them will restore the initial characteristics when EEPROM was set up.

author: floobydust
author_rank: Super Contributor
timestamp: July 12, 2021, 11:09:37 pm
content: It's not just the reference voltage that affects a function's calibration.Most of the DMM functions include the reference voltageplusadditional divider or shunt resistors, so the CAL values end up covering for all of these parts.You can try do a manual CAL with the multimeter, or read/modify the external EEPROM if it has one.OP was trying to super-calibrate his DMM, which I think is a poor idea because plain 1% resistors are not 0.01% resistors afterwards.

author: ialbert
author_rank: Newbie
timestamp: November 25, 2022, 05:03:33 pm
content: just for info.my an870 suddenly gives bad value. DC and Resistance.I shorted a jumper inside to activate CAL.Turn on the DMM. Set it to res/diode.Press the Select to SKIP those hex value.then for ex. you want to calibrate DC. set the knob there.then get a supply like for AN870. on DC set external supply to 1v, put the probe then it will show the reading. you can press the hold button to calibrate it for the right value.same with resistance.after that you can remove the jumper inside.and it works. now my an870 gives right value again.

author: ivo
author_rank: Regular Contributor
timestamp: September 16, 2024, 04:07:48 am
content: Quote from: ialbert on November 25, 2022, 05:03:33 pmThanks for this, now my AN870 reads 5.000V on my standard instead of 5.005V! Although the 'menus' were a bit f***y. Operator beware, it wants exact 1 x 10nvalues only (I think)! I tried to get it to cal 5V (thinking maybe the hold let you move the cal offset value around somehow) and almost stuffed my main voltage reading! It thought everything was half its value (5 is half of 10 I guess), and it really struggled to hold and take a 10V back exactly as a new cal reading. Got there in the end though.

author: ftv
author_rank: Newbie
timestamp: July 07, 2025, 12:06:27 pm
content: AN870 adjustment procedure that works for me:1. Short out JP2.2. Turn on the unit, it doesn't matter which position of the rotary switch. CAL will appear on the display.3. Now press the SELECT button twice briefly. The DC mV range will appear.4. Select, using the rotary switch and, if necessary, the SELECT button, which range you want to adjust.5. Apply the reference standard. You must always use a reference at exactly half the value of the range being adjusted - AN870 has 19999 digits, so for example use 1V on a 2V range, 10V on a 20V range, 100Ohm on a 200Ohm range etc.5. Press the HOLD button to save the calibration.

author: Aldo22
author_rank: Super Contributor
timestamp: August 27, 2025, 12:28:57 pm
content: Quote from: ftv on July 07, 2025, 12:06:27 pmThanks, that works really well!The only problem is finding a good voltage reference...

author: BeBuLamar
author_rank: Super Contributor
timestamp: August 27, 2025, 12:56:06 pm
content: In specs. 0.05% +3 counts.

author: Aldo22
author_rank: Super Contributor
timestamp: August 27, 2025, 01:15:18 pm
content: Quote from: BeBuLamar on August 27, 2025, 12:56:06 pmYes. I used the AD584L board for 10V.That should be accurate to 5mV.It wasn't absolutely necessary, but I think it's good that it can be adjusted so easily.

author: Aldo22
author_rank: Super Contributor
timestamp: September 21, 2025, 11:22:58 am
content: Does anyone know if A, mA, and μA can also be adjusted? If so, how?