Applent AT825 calibration - Page 1
Forum section: electronics / testgear

author: Veketti
author_rank: Regular Contributor
timestamp: March 26, 2023, 06:13:40 am
content: Dear All,I just bought some high precision resistors and noticed that my AT825 is showing 0.45ohm too small value. I confirmed this with bench multimeter by 4 wire measurement. Is there any way to adjust AT825 to show correctly, other than sending the meter to China? I've done the open and short calibration but that didn't help.Thank you in advance.

author: Bud
author_rank: Super Contributor
timestamp: March 26, 2023, 06:17:00 am
content: The high precision resistors are made in China by any chance?

author: Veketti
author_rank: Regular Contributor
timestamp: March 26, 2023, 06:31:16 am
content: Haha, no. Vishay Dale MR100 series from Digikey.

author: Kean
author_rank: Unknown
timestamp: March 26, 2023, 08:20:27 am
content: Did you try the "Short Correction" function?

author: Veketti
author_rank: Regular Contributor
timestamp: March 26, 2023, 08:45:47 am
content: Quote from: Kean on March 26, 2023, 08:20:27 amYes, as well as the open correction function.

author: Kean
author_rank: Unknown
timestamp: March 26, 2023, 09:24:07 am
content: Oh sorry, you did mention that.Have you tried different measurement frequencies, in particular the lowest setting?What do you measure with a direct short?I looked at buying one of these but I went with a different bench-top unit with higher frequency ranges in the end, so I cannot do any verification.

author: Veketti
author_rank: Regular Contributor
timestamp: March 26, 2023, 12:50:55 pm
content: Yes, I tried all the frequencies it has. Very little change.Short correction was done by clamping the measuring alligator clamps together.

author: TurboTom
author_rank: Super Contributor
timestamp: March 26, 2023, 03:27:47 pm
content: I'ld recommend to always do the short calibration on a short, high cross section pure copper wire with the kelvin clips, never by just hooking them up together. The latter method doesn't make sure that the sense terminals are always current-free while the wire method ensures that at least the probe current isn't flowing through any of the sense terminals but only through the wire.

author: Veketti
author_rank: Regular Contributor
timestamp: March 26, 2023, 04:28:13 pm
content: Ok, did it with short thick copper wire, but no differences in readings.

author: TurboTom
author_rank: Super Contributor
timestamp: March 26, 2023, 10:09:13 pm
content: Did you try to contact Applent's tech department? Regarding a different one of their products, they always tried to be very helpful and also provided some calibration instructions.https://www.anbai.cn/Contact

author: Kean
author_rank: Unknown
timestamp: March 27, 2023, 06:20:00 am
content: When you say "my AT825 is showing 0.45ohm too small value", what is the resistance you are measuring?You say they are high precision resistors, but an error of 0.45ohm could be a significant or insignificant percentage of the total value.When I asked "What do you measure with a direct short?", I meant what was the display value? Resistance and reactance?As TurboTom mentions, you should use 4W measurement with a shorting bar to ensure good contact but with separate contact points for source and sense. Doesn't the AT825 come with a shorting bar?

author: Veketti
author_rank: Regular Contributor
timestamp: August 19, 2023, 02:20:52 pm
content: I'll update this regarding the outcome. I contacted Anbai like suggested by TurboTom and they indeed were very helpful and willing to find out the issue. Outcome was that the meter was out of calibration. They could have adjusted it but as the meter was already over seven years old, they gave good offer for new meter. So it was no brainer to buy new as freight for sending the meter to China and back would be almost half of new meter price.