Is my calibration showing my tester is faulty?

[AngelSpark]

Hi lads,

I have a Megger 1552. I didn't really use it in the last couple of years. I was planning to get more into testing again, so sent it for calibration.

Unfortunately, it failed. I was told it requires a new side socket where the test leads plug into the tester. As the tester is old, Megger doesn't supply spare parts any more. At least the calibration guys didn't have any left with them. They didn't charge me.

Some days ago, when I was considering if it worth getting a new tester, I came across different company, that may take may old tester and deduct from the price of a new one. They also do calibration.

I figured if they take old testers, they may have spare parts. So I sent it for calibration and waited for their call that it failed. Surprising that didn't happen and I was issues a calibration certificate. The first test though didn't seemed like a pass to me. I have attached a photo of it. I contacted them and was told it was a typo. The correct testing voltage was 200, not 250. I was sent promptly a different calibration certificate. I have a few years old calibration from them and it is stated 250 on that test. I don't know if that was true or the guy just altered the page to fit into the tolerance specified.

So can someone tell me is my tester good or not? I don't want to use it for testing if it may not be giving correct results.

And what does the 17th edition comment next to the insulation resistance test mean? Is this normal? For reason I thought it should be 18th edition.

Many thanks

Angelo

 

[Lister1987]

Hi lads,

I have a Megger 1552. I didn't really use it in the last couple of years. I was planning to get more into testing again, so sent it for calibration.

Unfortunately, it failed. I was told it requires a new side socket where the test leads plug into the tester. As the tester is old, Megger doesn't supply spare parts any more. At least the calibration guys didn't have any left with them. They didn't charge me.

Some days ago, when I was considering if it worth getting a new tester, I came across different company, that may take may old tester and deduct from the price of a new one. They also do calibration.

I figured if they take old testers, they may have spare parts. So I sent it for calibration and waited for their call that it failed. Surprising that didn't happen and I was issues a calibration certificate. The first test though didn't seemed like a pass to me. I have attached a photo of it. I contacted them and was told it was a typo. The correct testing voltage was 200, not 250. I was sent promptly a different calibration certificate. I have a few years old calibration from them and it is stated 250 on that test. I don't know if that was true or the guy just altered the page to fit into the tolerance specified.

So can someone tell me is my tester good or not? I don't want to use it for testing if it may not be giving correct results.

And what does the 17th edition comment next to the insulation resistance test mean? Is this normal? For reason I thought it should be 18th edition.

Many thanks

Angelo

The 17th comment may just be thier software not updating the text.

 

[telectrix]

strange. once had exactly same with 1553. failed due to the 4mm sockets giving erratic readings on continuity.. found that if the leads were inserted 2mm short of fully home, readings were spot on. cotton bud and a bit of switch cleaner cured it. took it back and it passed. it's no big deal to replace these sockets. standard part. inside the unit, they are paralled with the socket that you use for plugging in the 1363 lead, so a comparison can be made between the 2. as lister says, the teaster's cert. is probably notupdated software.

have heard of instances where the wires on the back of these sockets are dry-jointed.if your sockets are in fact iffy, anyone with soldering skills can fix. tha hardest part is opening the case. you have to peel off the front to access the 4 screws underneath.

company called The Calibration Centre at Stafford do reasonably priced repairs. probably under £100 to fix.

 

[Wilko]

Hi - not expert on testing testers, but the software for your cert looks to be crook, not your mft.

The mft generates a DC voltage to perform the insulation test. There are 3 target voltages for IR testing, being the usual 250V, 500V and 1000V. The calibration test is looking at how close is your MFT‘s test voltage to these targets. Yours are all within their listed target range, so it’s a pass.

But I don’t know why they’ve got 550V and 1100V listed as Applied Value, when it’s not intended to be that. It should be listed as 500V and 1000V, in my opinion.

 

[telectrix]

the applied value is the actual voltage put out by the meter on each range. on that cert. it appears that the tester is outputting 10% over voltage on the 500 and 1000V ranges.

 

[Julie.]

There are a number of simple tests you can do, firstly buy some 1% resistors, say 10M Ohm, 100M Ohm etc - since these are 1% (and you can get better ones but more expensive) they are in the same order of magnitude of error as your MFT, so compare against these - doesn't replace a cert, but will allow sanity checking.

You can do the same for Ze/Zs tests - get a 1% 0.1 Ohm resistor and just carry out a Zs on one particular socket, then insert the 0.1 Ohm resistor and repeat the test - your result should read 0.1 Ohm higher - you can try any of the 2w/3w high/low current ranges (subject to RCD protection on the socket outlet) and again you can try other values of resistor etc.

It's also possible to check resistance ranges by measuring these resistor values

As for voltage measurement (of the insulation resistance test, or the voltage range) you can use another calibrated multimeter or whatever - but generally not an MFT as it isn't a high resistance so will impact the IR test voltage.

The only thing to be careful with is the results - a 100M resistor could be 99 - 101M ohm (+/-1%) plus if your instrument is say +/-2% so it could be 97-103M ohm and still be valid.

This addition of errors is noticeable when comparing meters, one reads 229.5V, another 253.5V - but on a 230V supply - so is the first correct and the second wrong?

Nope, the voltage is actually 5% up on nominal (241.5V) and BOTH meters are reading within their 5% tolerance - one at the lower end and one at the higher.

these just allow sanity checking - doesn't replace proper calibration.

 

[davesparks]

. The first test though didn't seemed like a pass to me. I have attached a photo of it. I contacted them and was told it was a typo. The correct testing voltage was 200, not 250. I was sent promptly a different calibration certificate. I have a few years old calibration from them and it is stated 250 on that test. I

The first test on the sheet is current of the continuity test, not voltage.
This should be 200mA so the paperwork you have shown with 250ma on it is indeed wrong.

 

[AngelSpark]

Thank you all for your input. Quite interesting, I haven't put much thought on the result before.

I will give the guys at the Calibration Centre at Stafford a call and see what they can do.

Meanwhile I may try to play around with it and see if I can open it to have a look.

Many thanks

 

[telectrix]

Thank you all for your input. Quite interesting, I haven't put much thought on the result before.

I will give the guys at the Calibration Centre at Stafford a call and see what they can do.

Meanwhile I may try to play around with it and see if I can open it to have a look.

Many thanks

if you pm me before you attempt this, i can advise as i have opened and repaired3 1552/3 s. just to say that they were all simple repairs. opening the cases took far longer than the repairs. 1 was afuse, and 2 were simple soldering repairs. in a past life i was a TV repair man.