Higher-accuracy low Ze test procedure

[Engineer54]

I dont see this technique helping.

Lets say the Impedance is 0.02 ohms, at 230 V this equates to 11.5kA.

Now if we introduce an impedance of 0.5 ohms, our circuit is now 0.502 ohms.

At 0.502 ohms standard meters will have a 10% +/- and a 5 digit error +/- around the 0.5 area.

So this equates approx to a +/- of 0.1 ohm, so even with the 0.5 ohm added the reading could be 0.6 ohms or 0.4, a differnace of 0.2 ohm's.

Cheers

So without going into another pointless in depth discussion so you can prove a point, when was the last time you applied the +/- 10% and 5 digit error or so, to any value that you measured with you're MFT/EFI tester, and recorded that amended value on a report sheet??

The above method is just a means of enabling a relatively standard MFT/ELI meter to more accurately measure values that are very close to it's ultimate limit, nothing more, nothing less!!

 

[GEOFF S]

So without going into another pointless in depth discussion so you can prove a point, when was the last time you applied the +/- 10% and 5 digit error or so, to any value that you measured with you're MFT/EFI tester, and recorded that amended value on a report sheet??

The above method is just a means of enabling a relatively standard MFT/ELI meter to more accurately measure values that are very close to it's ultimate limit, nothing more, nothing less!!

I Dont, but then i wouldnt add a 0.5 ohm impedance to the circuit either, chocolate fireguard!

Well is not going to give you a more accurate result, how can it, when even with the added 0.5 ohm impedance you could get a negative result!

The example i gave was 0.02, now the meter error could be 0.2 ohms, so far from accurate, misleading infact!

Cheers

 

[Engineer54]

I Dont, but then i wouldnt add a 0.5 ohm impedance to the circuit either, chocolate fireguard!

Well is not going to give you a more accurate result, how can it, when even with the added 0.5 ohm impedance you could get a negative result!

The example i gave was 0.02, now the meter error could be 0.2 ohms, so far from accurate, misleading infact!

Cheers

I'm not going to even bother going there....

 

[mrloy99]

Lets say the Impedance is 0.02 ohms,

''Now if we introduce an impedance of 0.5 ohms, our circuit is now 0.502 ohms.''

Hmm is it? 0.5 plus 0.02 is 0.52

sorry old post I know....I personally prefer to use a resistor with value of 1 ohm as its a lot easier to subtract at the end

Cheers[/QUOTE]

 

[davesparks]

I Dont, but then i wouldnt add a 0.5 ohm impedance to the circuit either, chocolate fireguard!

Well is not going to give you a more accurate result, how can it, when even with the added 0.5 ohm impedance you could get a negative result!

The example i gave was 0.02, now the meter error could be 0.2 ohms, so far from accurate, misleading infact!

Cheers

If you look at the specification of a loop tester such as the megger offerings you'll see that their accuracy is stated as being higher within a certain band of resistances so adding a dummy resistor in can put the test results into the more accurate part of the range.

 

[David Marshall]

Lets say the Impedance is 0.02 ohms,

''Now if we introduce an impedance of 0.5 ohms, our circuit is now 0.502 ohms.''

Hmm is it? 0.5 plus 0.02 is 0.52

sorry old post I know....I personally prefer to use a resistor with value of 1 ohm as its a lot easier to subtract at the end

Cheers

[/QUOTE]
I can't see the point in this method, it's a total waste of time. Just measure ze and move on adding a resistance to the figure only to subtract it will only give you what you would get anyway. If you get 0.02 just record it and recommend suitable mcbs that's all you need to do.

 

[davesparks]

I can't see the point in this method, it's a total waste of time. Just measure ze and move on adding a resistance to the figure only to subtract it will only give you what you would get anyway. If you get 0.02 just record it and recommend suitable mcbs that's all you need to do.[/QUOTE]

The point is to make use of the most accurate part of the test meter's range.

 

[David Marshall]

I can't see the point in this method, it's a total waste of time. Just measure ze and move on adding a resistance to the figure only to subtract it will only give you what you would get anyway. If you get 0.02 just record it and recommend suitable mcbs that's all you need to do.

The point is to make use of the most accurate part of the test meter's range.[/QUOTE]

How accurate do we need to be, I'm happy with the approved method described in GN3 which in all fairness is the only method recommended, why complicate this test. My advise is to stick to the approved method because at the end of the day nobody can fault you for complying with your training and non statutory regulations,
This is my final post on this subject, please don't reply as I will not respond.
Thanks David