Author Topic: Adjustment of Metrahit 18s and 18c ? (Read 27824 times)

giovannirat · « **on:** June 15, 2015, 07:33:41 pm »

I own a Gossen Metrahit 18s multimeter and a Siemens B1108 calibrator, which is an OEM of Gossen Metrahit 18c calibrator.

At least the 18s multimeter needs an adjustment. Unfortunately i could not find any service manual and the Gossen-Metrawatt company was not willing to send me a service manual or some hints, how to adjust the multimeter

Really disappointing .....

There are 5 trim-pots on the back oft the multimeter (red circles) , but i have no idea which one is adjusting what.

A completely different story is the calibrator, which has no trim-pots. I guess in this case the calibration or adjustment is done by software ?

I would appreciate, if someone could send me a service manual or even give hints how to adjust the multimeter or the calibrator.

Many thanks

robert_ · « **Reply #1 on:** August 18, 2015, 11:52:10 pm »

Datasheet says:
Calibration
The multimeters of the METRAHit S series can be calibrated auto-
matically via the RS-232 data interface with the aid of the multi-
function calibrator METRAtop 90C and the METRAwin 91 soft-
ware.

Metrahit 18s is a surprisingly good meter btw. While the 12s-16s are more like electricans meters with not exactly good precision (0,25% or worse) but high robustness, the 18s is specified for 0,05% +3dgt. Still you can often get a functional 18s for less than 50eur on ebay. Much better that to spend the same 50eur on something from Uni-T...
I have both a older and never model, the older is only marked with 1000V max. while the newer one is rated 600V Cat III. Layout and protection components are identical on both, so i guess the older version simply wasmade before the relevant IEC standard came out. The fuses shold be 600V or 1kV DC rated, on one i bought used the 1.6A fuse was replaced by solder wire, and the 16A fuse with a screw

sorenkir · « **Reply #2 on:** August 19, 2015, 09:44:55 am »

I don't know what's behind the black shield of the 18s, but position of adjustments seems similar to MetraHit 16S (to be checked before doing anything!)
Attached is the cal. procedure for the 16S.
Michel.

robert_ · « **Reply #3 on:** August 19, 2015, 10:18:41 pm »

Id be careful here, 12s-16s indeed are quite similar, 18s is a rather different instrument (30k count instead of 3k, much tighter specifications) so i would not expect these trims to be identical. Normal calibration is done via software.

giovannirat · « **Reply #4 on:** August 20, 2015, 02:29:51 pm »

Thank you all for the feedback

As robert_ wrote the 18s seems to be a bit different.

So if somebody has a service manual or something similiar i would be grateful for sharing it.

Any other information regarding calibration of Metrahit 18s or 18c also welcome.

Thanks

retiredcaps · « **Reply #5 on:** August 20, 2015, 04:59:19 pm »

Quote from: giovannirat on June 15, 2015, 07:33:41 pm

At least the 18s multimeter needs an adjustment.

What needs adjustment?

A while back I saw this video

suggesting that using freeze spray would help determine what the pot does on the multimeter. I don't know if this is a good or bad idea so decide for yourself.

ulix · « **Reply #6 on:** August 24, 2015, 08:50:42 pm »

Hi,
I know for sure that for example the Metrahit World, 2, 24, Xtra, Base, Tech (...) are all calibrated via infrared/ RS-232.
I think with the 18 is it the same.

They won't get you anything to self-adjust your meter from gmc. You/ We have to read the mcu

I looked myself for some adjustment manuals, but you won't find anything...

MatthiasBerlin · « **Reply #7 on:** October 25, 2015, 12:00:17 pm »

Quote from: robert_ on August 19, 2015, 10:18:41 pm

Id be careful here, 12s-16s indeed are quite similar, 18s is a rather different instrument (30k count instead of 3k, much tighter specifications) so i would not expect these trims to be identical. Normal calibration is done via software.

The Metrahit 1x series (except the 18C calibrator, it seems) have only an unidirectional IR interface for sending, so there is no way to calibrate them by software, you could just use the IR output during the calibration process to log the calibration results. I guess that's what they're doing because these devices usually come with detailed calibration certificate.

The 12s-16s also offer 30k count via the IR interface, so it would just require mainly a different display with one more digit, possibly modified software and better components to create a 18S on base of the other multimeters. However, I have no idea if this was done or if it is a different construction.

If I were giovannirat, I'd mark the position of the trimmers and then modify the position a bit one by one according to the calibration instruction to see if the function of each one matches the one of the 12S-16S.

The Metrahit 2x and Starline Series (X-Tra, etc.) are a different story, they seem to be calibrateable by software.

Brutzler · « **Reply #8 on:** December 31, 2015, 11:43:27 am »

Hi,

I'm new to this forum and I thought you could help me to get my Metrahit 15S working.
It has some problems with measuring resistance and capacitance, Volts and Amps measurement works fine.
I got this meter for free and I already replaced the 1,6 A fuse for the 300mA range.
The problem is that theres one blown component inside which I don't know the value of.
And theres no way to measure it anymore

At first glance, I thought it could be a SMD cap which they bodged into a THT part

But after some tests, I found out that it must be a resistor.
I replaced it with a 50k pot, compared the displayed values with a FLUKE 177 and ended up with a value of about 1.8k.
It would be nice to replace this part with the right value, to get the meter properly working again.

Regards
Brutzler

Le_Bassiste · « **Reply #9 on:** December 31, 2015, 01:17:53 pm »

Quote from: giovannirat on June 15, 2015, 07:33:41 pm

I own a Gossen Metrahit 18s multimeter and a Siemens B1108 calibrator, which is an OEM of Gossen Metrahit 18c calibrator.

At least the 18s multimeter needs an adjustment. Unfortunately i could not find any service manual and the Gossen-Metrawatt company was not willing to send me a service manual or some hints, how to adjust the multimeter
Really disappointing .....

There are 5 trim-pots on the back oft the multimeter (red circles) , but i have no idea which one is adjusting what.

A completely different story is the calibrator, which has no trim-pots. I guess in this case the calibration or adjustment is done by software ?

I would appreciate, if someone could send me a service manual or even give hints how to adjust the multimeter or the calibrator.

Many thanks

the three pots on the left hand side are trim-caps. these are most probably used to adjust gain flatness on AC ranges, so these shouldn't be touched

the two pots on the right hand side seem to be normal trim-pots. i suspect that the multimeter is using a standard DMM-chip from maxim. try to remove the shield to find the part number of the chip. then, you may find the corresponding app-note for that chip that will most likely reveal the usage of those pots.
(for example, the Gossen M2008 is using a MAX133 3-3/4 digit DMM chip and an Analog Devices AD636 for the TRMS converter)

retiredcaps · « **Reply #10 on:** December 31, 2015, 09:48:42 pm »

The best 15S picture I could find with a brief search is

http://img834.imageshack.us/img834/2193/img20130323wa0008b.jpg

Given that the 15S has its ground and Volt jack on the left hand side, your component might be a blown PTC. All the bigger name brand manufacturers have some sort of input protection and this may be a PTC.

Here is a picture of a green colored PTC from a Fluke 75 II meter. The PTC in the Fluke is 1.0k ohm +/- 40%. Most PTCs that I have seen in are in the 1.0k to 1.5k ohm range.

I will look again later, but right now I have to work on a car battery charger that is dead.

retiredcaps · « **Reply #11 on:** January 01, 2016, 05:14:06 am »

BTW, just taking a closer look at the pcb, there seems to be no input protection on this 15S?

If that bad component is a PTC, that is the only input protection. I don't see a varistor/spark gap, no big current limiting resistors, diode bridges, isolation slots, etc. Very disappointing.

The Metrahit 16S has the same grey colored PTC component (in between the two fuses) as per

https://www.eevblog.com/forum/chat/nice-catch-or-not-3x-gossen-metrawatt-metrahit-16s/

as does the 14A

https://sigrok.org/wimg/6/69/Gmc_metrahit_14a_inside_2.jpg

and 18A

https://sigrok.org/wimg/2/25/Metrahit_18S_2.jpg

The 16S, 18A and 14A also all seem to lack input protection as well?

Brutzler · « **Reply #12 on:** January 01, 2016, 12:09:45 pm »

Hi,

Yeah, according to the schematic (which Matthias has been kind enough to send me) it's most likely a PTC.
Wikipedia tells me the same :
https://commons.wikimedia.org/wiki/File:PTC-Resistor.svg
The "2k" seems like the resistance at 20°C, or something. This is pretty close to the value I found out (1.8k).

I'll try to contact Gossen Metrawatt for more info.

Regards
Brutzler

retiredcaps · « **Reply #13 on:** January 01, 2016, 06:24:03 pm »

Quote from: Brutzler on January 01, 2016, 12:09:45 pm

Yeah, according to the schematic (which Matthias has been kind enough to send me) it's most likely a PTC.

@MatthiasBerlin,

Can you please post the entire schematic so I can see, for learning purposes, how the rest of the multimeter looks?

Dachpappe · « **Reply #14 on:** January 02, 2016, 02:54:26 pm »

Hi,
I just took my two Metrahits apart to look for the component, but sadly the input protection in the 23S is quite different and on the PTC in my 18s are no markings. In-circuit i'm getting 1,71k resistance on the Part in the 18s.
In the "Spoerle Components Guide" I could only find PTCs with a U_max of 265V. They also come in a smaller package, so the ones used in the Gossen multimeters might be special ones with a significantly higher U_max.

retiredcaps · « **Reply #15 on:** January 02, 2016, 11:53:06 pm »

A couple of years ago, I bought an used/abused Fluke 77 III. When I initially checked it out, everything seemed to work fine.

A few months later, I measured a 100 ohm resistor and discovered it was around 98 ohms (out of spec on the 320 ohm range). I then discovered that the 32M range was out of spec as well. Since I have never used this meter on any high energy or mains circuitry, I can only conclude that the previous owner damaged the meter and did not disclose it on the ebay listing.

After some testing, I discovered that the PTC was measuring 100k ohm instead of the 1k ohm. I replaced the PTC with a 1k ohm carbon film resistor that measured 970.8 ohm, as a test, and now all ranges are within spec.

What I'm hinting at is that whether the PTC is 1.8 or 1.71 or 2k ohm, it is likely not to affect the resistance measurements that much. In my example above, even though the PTC was 100x times more than its rated value, the 320 and 32M ohm measurements were not that far off and all the other ranges in between (3.2k, 32k, 320k, 3.2M) were fine.

Dachpappe · « **Reply #16 on:** January 03, 2016, 01:01:38 am »

Well, this is actually a very interesting fact!
Do you have any suggestions where to order proper PTCs with matching voltage rating and tripping current/time?
What type did you use for fixing you Fluke?

retiredcaps · « **Reply #17 on:** January 03, 2016, 07:16:22 am »

Quote from: Dachpappe on January 03, 2016, 01:01:38 am

Do you have any suggestions where to order proper PTCs with matching voltage rating and tripping current/time?

It depends on what the voltage rating of the PTC is. It is not listed on the schematic.

Quote

What type did you use for fixing you Fluke?

I ended up using another PTC from another dead Fluke meter (the part was identical to the bad one). The only 3rd party part that I found with a 1.1k ohm and 1000V rating is YS4020, but no one sells or stocks it.

http://www.mouser.com/ds/2/18/amphenoladvancedsensors_YS4020-492783.pdf

KlausF · « **Reply #18 on:** February 11, 2019, 12:57:51 pm »

Good job, thank u for mentioning the PTC. That seems to be the problem with my Metrahit, too.

retiredcaps · « **Reply #19 on:** February 11, 2019, 06:21:14 pm »

Quote from: retiredcaps on January 03, 2016, 07:16:22 am

I ended up using another PTC from another dead Fluke meter (the part was identical to the bad one). The only 3rd party part that I found with a 1.1k ohm and 1000V rating is YS4020, but no one sells or stocks it.

Digikey and Mouser have it in stock now

https://www.digikey.ca/product-detail/en/amphenol-advanced-sensors/YS4020/235-1493-ND/4250581

eric.niu · « **Reply #20 on:** February 26, 2019, 10:36:30 am »

Hi guys, I'm new here, I know this thread is old, any update on 18s calibration? I have 18s but need to calibrate

eric.niu · « **Reply #21 on:** December 02, 2019, 11:00:16 am »

check it out
https://www.eevblog.com/forum/testgear/calibrate-your-metrahit-18s-without-specific-software-i-figured-it-out/


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Author Topic: Adjustment of Metrahit 18s and 18c ? (Read 27824 times)

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