looking for MASTECH MS8229 calibration procedure

[cyberfuzzy]

Hello,

I have several MASTECH MS8229 multimeters. But some of them are out of range. Unfortunately I can't find a calibration procedure for it. I asked the manufacturer for it but it seems so that they don't want to send me that information.

So I opened it up and tried to turn the trim pots. But I wasn't able find out what each potentiometer is for. There are some pictures of the pots on that page:
https://www.eevblog.com/forum/testgear/re-brand-of-mastech-ms2882()-from-harbor-freight-(item-98674)/

Has anyone of you a calibration procedure for the MASTECH MS8229? Or did one of you find out what the individual pots are for?

Thanks a lot!

Cyberfuzzy

[joeqsmith]

I posted most of them here:

https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/30/

[cyberfuzzy]

Thank you joeqsmith. I'm going to try to calibrate it now :-)

[retiredcaps]

I have several MASTECH MS8229 multimeters. But some of them are out of range.

I'm curious about what is actually out range.  Is it DCV or resistance?  How much is it out of range by?

[cyberfuzzy]

@retiredcaps: I don't really know how much it is out of range because I do not have high end multimeters, voltage standards and so on. But to get an idea of it I did some measurements with four multimeters.

The number in front of the following results is the number of the multimeter as you can see here:



Multimeter 1: MASTECH MS8229 (original condition)
Multimeter 2: MASTECH MS8229 (original condition)
Multimeter 3: UNI-T UT58C (original condition)
Multimeter 4: MASTECH MS8229 (opened, trim pots turned)


Here are the results of some measurements:

DC Voltage:
(All multimeters connected to the same potential.)
1. 190.5 mV
2. 190.7 mV
3. 189.9 mV
4. 190.7 mV

1. 1.884 V
2. 1.889 V
3. 1.883 V
4. 1.894 V

1. 19.52 V
2. 19.61 V
3. 19.51 V
4. 19.70 V

1. 60.0 V
2. 60.3 V
3. 60.0 V
4. 60.4 V


AC Voltage:
(All multimeters connected to the same potential.)
1. 1.043 V
2. 1.043 V
3. 1.044 V
4. 1.037 V

1. 18.87 V
2. 18.90 V
3. 18.90 V
4. 18.87 V

1. 194.5 V
2. 195.1 V
3. 199.8 V
4. 194.0 V

1. 277.2 V
2. 278.1 V
3. 278 V
4. 276.6 V


Frequency:
(All multimeters connected to the same potential.)
1. 49.99 Hz
2. 49.99 Hz
3. 0.047 kHz
4. 49.99 Hz

1. 0.999 kHz
2. 0.999 kHz
3. 1.000 kHz
4. 0.999 kHz

1. 18.99 kHz
2. 18.99 kHz
3. 19.06 kHz
4. 18.99 kHz


DC Current:
(All multimeters connected in series.)
1. 35.91 mA
2. 36.20 mA
3. 36.0 mA
4. 36.37 mA

1. 188.2 mA
2. 189.3 mA
3. 188.6 mA
4. 190.1 mA

1. 2.912 A
2. 2.933 A
3. 2.94 A
4. 2.931 A


AC Current:
(All multimeters connected in series.)
1. 0.402 A
2. 0.404 A
3. 0.41 A
4. 0.400 A

1. 3.024 A
2. 3.034 A
3. 3.06 A
4. 3.015 A


Resistance:
(I used a 1.82 kOhm, 1% resistor. LCR/ESR-Meter measured 1.8187 kOhm.)
1. 1.818 kOhm
2. 1.816 kOhm
3. 1.817 kOhm
4. 1.820 kOhm

[retiredcaps]

AC Voltage:
(All multimeters connected to the same potential.)
1. 1.043 V
2. 1.043 V
3. 1.044 V
4. 1.037 V

You don't necessarily need a voltage standard, but a quick look through your readings, I would say all 4 meters are within their specifications.  For the above measurements in your picture, the spec for ACV is 0.8% + 3 counts.  Assuming 1.043 is the "correct" measurement, all the meters are easily within the 0.8% +3 counts.

Even the best meters will differ 1mV or 2mV, but be within their respective specifications. 

In your original post, I thought you were getting readings like 1.043 on one meter and 1.542 on another meter.

[retiredcaps]

DC Voltage:
(All multimeters connected to the same potential.)
1. 19.52 V
2. 19.61 V
3. 19.51 V
4. 19.70 V

The DCV for the Mastech is 0.7% + 2 counts.  The UT58C is 0.5% + 1 count.

If the 19.52V is the correct reading, then #4 is slightly out of spec.

19.52 x 0.7%  = 0.13664 = 0.14 => 0.14 + 2 counts = 16 counts.

So 19.52 + 0.16 = 19.68 (upper bound).

PS. I haven't done the calculations for your other ranges, but given the internal build quality and components of your meters, for most purposes, it should be good enough.  To get something more accurate, the meter has to have some high quality precision hybrid resistor network and/or software stored calibration offsets for each range.

[Lightages]

Really, for the price of cheap voltage references right now, there is no reason to not have one to check your meters:

http://www.ebay.com/itm/AD584KH-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-Simpl-/181219600361?hash=item2a3187a7e9

http://www.ebay.com/itm/KKMOON-Accuracy-Voltage-Reference-Module-AD584kH-4-Channel-2-5V-7-5V-5V-10-NEW-/131566638421?hash=item1ea1fb9555

and there are more useful ones for multimeters at:
www.voltagestandard.com

[retiredcaps]

1. 194.5 V
2. 195.1 V
3. 199.8 V
4. 194.0 V

Wow, the UT58C reading is way off compared to the other 3.  Since the UT58C is a 2,000 count meter, this reading is close to full scale.

[cyberfuzzy]

Wow, the UT58C reading is way off compared to the other 3.  Since the UT58C is a 2,000 count meter, this reading is close to full scale.

Maybe that is because it was not a perfect sine wave? I used a transformer on mains voltage for that measurement.

[cyberfuzzy]

I repeated the measurement with 198 V and 130 V. All multimeters were connected the same way as yesterday. It looks much better now.

I think the deviation yesterday could be of a bad sine wave or maybe the voltage changed and the update rate of the UT58C is to slow?

Today's results:

AC Voltage:
1. 198.2 V
2. 198.8 V
3. 198.7 V
4. 197.7 V

1. 130.4 V
2. 130.9 V
3. 130.9 V
4. 130.0 V

The scope measures 131 V. But it is definitely not a perfect sine wave as you can see here:

[joeqsmith]

Thank you joeqsmith. I'm going to try to calibrate it now :-)

No problem.  Glad to help.   Let me know if you figure out what the other pots are for. 

[giorgiovi]

Hi,
do you have procedure calibration for MS8229?
Thanks

[giorgiovi]

Has anyone of you a calibration procedure for the MASTECH MS8229?