Inductive cause of leaks to earth

[JohnW2]

Sadly no info, it's badged as 'BT no. 5' (and the printed label on the back is pretty much worn clear) which means nothing as BT would put out a spec and manufacturers would provide samples which became type approved and purchased(or not). We alway hoped the MeterMultiRange no. 1 would be the Wayne Kerr version as it was the best of the selection BT puchased, and Linstrom for cutters, Wilson for 81's etc.

Pity! ... and still very strange.

You described it as a 20A/200A meter. Does that mean that it has two switchable ranges?

Are you saying that on the 20A range, it displays "mA"? If so, how many digits is it displaying and what would you expect it to display if the current being measured were, say, 19.999 A on that range? Does it really have enough digits to display "19999.0" (which is what one would expect in the light of the readings you have been reporting)? ... or is it somehow actually 'auto-ranging' (within the '20A' range) and switching to a different range (and displaying "mA") when it finds that it is measuring a current much lower than 20A.

It does seem strange!

Kind Regards, John

 

[JohnW2]

If I understand correctly, the dramatic differences between results with your DMM on its 200 mA and 200 μA ranges seem to 'say it all'.

Easily explained by very low voltages and differences in meter resistance.

I don't really get that.

Neither on the 200 mA nor the 200 μA range should the resistance of the current meter be high enough to affect the current flowing in the circuit appreciably (let alone up to a 10-fold difference!) - otherwise it would be pretty useless as a current measuring instrument!

Kind Regards, John

 

[SUNRAY]

And to follow this up a little a 1MΩ resister on 24V transformer measured as 1,000,2xxΩ & 25.3V Where xx hovered around 40
200A clamp=0.1A, 20A clamp=4.6mA but these are right beside the transformer. Changed to 0.0A & 3.9mA a metre away.
20mA range=0.21mA, 200μA range 25.4μA.


The 200μA range seems to be holding up, 2x 1MΩ (999,98xΩ hovered around 5) in series measured 12.6μA and parallel 50.6μA


My big apologies, in previous posts I quoted 200mA range (which has a 0.1mA resolution). Therefore previous reference to 200mA range should read 20mA range.

 

[Harry Bloomfield]

Neither on the 200 mA nor the 200 μA range should the resistance of the current meter be high enough to affect the current flowing in the circuit appreciably (let alone up to a 10-fold difference!) - otherwise it would be pretty useless as a current measuring instrument!

Suggest you try (with a second instrument) measuring the resistance of the two ranges.

 

[SUNRAY]

Pity! ... and still very strange.

You described it as a 20A/200A meter. Does that mean that it has two switchable ranges?

Are you saying that on the 20A range, it displays "mA"? If so, how many digits is it displaying and what would you expect it to display if the current being measured were, say, 19.999 A on that range? Does it really have enough digits to display "19999.0" (which is what one would expect in the light of the readings you have been reporting)? ... or is it somehow actually 'auto-ranging' (within the '20A' range) and switching to a different range (and displaying "mA") when it finds that it is measuring a current much lower than 20A.

It does seem strange!

Kind Regards, John

It's 3.5 digit on 20 A range it will display xx.x A or xxx.x mA and on 200A range xxx.x A

The 20mA and 200μA ranges I refer to are on a different non clamp 3.5 digit meter.

 

[SUNRAY]

Suggest you try (with a second instrument) measuring the resistance of the two ranges.

The shunt is a pair of parallel diodes so will be non linear.

 

[JohnW2]

Suggest you try (with a second instrument) measuring the resistance of the two ranges.

It'd SUNRAY, no me, who needs to try that.

Kind Regards, John

 

[JohnW2]

It's 3.5 digit on 20 A range it will display xx.x A or xxx.x mA and on 200A range xxx.x A

OK - so, as I asked, when on the 20A range does it 'auto-range' and automatically switch to displaying "xxx.x mA" when it finds that it is measuring a current less than 1 A?

The 20mA and 200μA ranges I refer to are on a different non clamp 3.5 digit meter.

yes, I realise that - although you previously said 200 mA (not 20 mA) and 200 μA ranges.

Kind Regards, John

 

[SUNRAY]

OK - so, as I asked, when on the 20A range does it 'auto-range' and automatically switch to displaying "xxx.x mA" when it finds that it is measuring a current less than 1 A?
yes, I realise that - although you previously said 200 mA (not 20 mA) and 200 μA ranges.

Kind Regards, John

Yes except it's max 199.9mA, not 999.9

That was my bad, reading back the figures I listed it had to have been the 20mA range.

 

[JohnW2]

Yes except it's max 199.9mA, not 999.9

Yes, sorry, I forgot that it was a 3½ digit display.

So, although it does not 'auto-range' between the 20A and 200A ranges, on the 20A range it effectively auto-ranges between an actual 20A range and a 200 mA range? Is that correct?

If so, as I've said, it's different from any "20A/200A"! (or similar) clamp meter that I have ever had any dealings with, or awareness of!

Kind Regards, John

 

[SUNRAY]

Yes, sorry, I forgot that it was a 3½ digit display.

So, although it does not 'auto-range' between the 20A and 200A ranges, on the 20A range it effectively auto-ranges between an actual 20A range and a 200 mA range? Is that correct?

If so, as I've said, it's different from any "20A/200A"! (or similar) clamp meter that I have ever had any dealings with, or awareness of!

Kind Regards, John

Yes that sums it up. The same thing happens with the 600v & 200V ranges and resistance 20MΩ & 200Ω are fixed but 2MΩ auto ranges.

I've handled a selection of multimeters, both digital and analogue in the different fields of work I've found myself in and of course the early ones were all manual, the first couple had a series of sockets for the different ranges rather than switches but since then I've handled rediculous numbers of test meters (the BT MMR no.1 I mentioned before for example came in at least 5 different makes and even those sometimes would have variations, one version included a 1Hz to 32KHz sine/square wave sig gen, freq counter and LMS). Initially I didn't like autoranging as I'd miss the range had changed, these days the indicator is letters and not just a little dot somewhere vaguely near the printing beside the display.

The surprise element vanished a long time ago.

 

[Harry Bloomfield]

Initially I didn't like autoranging as I'd miss the range had changed, these days the indicator is letters and not just a little dot somewhere vaguely near the printing beside the display.

I have an amazingly tiny one, which not only autoranges its range, but also makes a usually intelligent decision on what you are trying to measure. It does auto-switching between AC, DC, capacitance, resistance and frequency.

 

[SUNRAY]

I have an amazingly tiny one, which not only autoranges its range, but also makes a usually intelligent decision on what you are trying to measure. It does auto-switching between AC, DC, capacitance, resistance and frequency.

I worked with a guy that had somethig similar but I confess I struggled with it wanting to do a different measurement to what I wanted, I was trying to measure resistance of a sensor, however being a coil wrapped round the metal object it was sensing the temp of it wanted to measure to inductance, looking for a pair in a multicore by measuring voltage it tried to measure capacitance. It needed to include the ability to overide the auto facility.

This was not much bigger than a Swan Vesta box, nice big clear display (which I could read without glasses), effective magnet and hanging clip, as a volt meter I couldn't fault it. IIRC there was no current range.

 

[Harry Bloomfield]

I worked with a guy that had somethig similar but I confess I struggled with it wanting to do a different measurement to what I wanted, I was trying to measure resistance of a sensor, however being a coil wrapped round the metal object it was sensing the temp of it wanted to measure to inductance, looking for a pair in a multicore by measuring voltage it tried to measure capacitance. It needed to include the ability to overide the auto facility.

This was not much bigger than a Swan Vesta box, nice big clear display (which I could read without glasses), effective magnet and hanging clip, as a volt meter I couldn't fault it. IIRC there was no current range.

Mine just has a single button, runs on a button cell. I bought it because it was such a novelty. One long press to turn it on in auto mode, then more presses lock it to a mode. It was handy to take along to the radio rallies (car boot sales of the amateur radio world), for checking out potential purchases.

 

[SUNRAY]

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