Fluke T50 Voltage/Continuity tester

[JohnW2]

Someone asked me about an issue he had had with testing for 'continuity' using a Fluke T50 Voltage/Continuity tester. In essence, he was getting an indication of 'continuity' when he wasn't expecting it, and it seemed probable that the explanation was that there were probably some 'connected loads' whose resistance was being measured/detected by the tester.

This led me to wonder how low the resistance had to be for this device (which apparently has a 'bleeper' and just one 'continuity LED') to declare 'continuity'. The user manual is not all that clear, merely indicating that the 'resistance range' for continuity testing is 0 - 200 kΩ. If that means that it will indicate 'continuity' (bleeping and lighting up its LED) with a resistance as high as 200 kΩ, that would seem to be verging on the ridiculous, and rather limiting its value as a useful 'continuity tester'.

I wonder if any of you have, or know about, the T50 - and, if so, if you know what is the maximum resistance that it will interpret as 'continuity'?

Kind Regards, John

 

[Iggifer]

I had a T150 or whatever the model was at the time, worst two probe tester ever, purely because of the fixed probe - snapped off pretty quickly.

It's only powered by 2xAAA batteries don't forget and the test current for the T90, at least is 5 μA, so I wouldn't expect it to be able to detect much above their specs (if it can even detect all the way up to 200 kΩ) a Megger 1552 uses about 2mA I think, 400 times more!

What kind of parallel paths are we talking?

 

[JohnW2]

I had a T150 or whatever the model was at the time, worst two probe tester ever, purely because of the fixed probe - snapped off pretty quickly. It's only powered by 2xAAA batteries don't forget and the test current for the T90, at least is 5 μA, so I wouldn't expect it to be able to detect much above their specs (if it can even detect all the way up to 200 kΩ) a Megger 1552 uses about 2mA I think, 400 times more!

I think that you may have misunderstood what I was saying. I am not talking about detecting high resistances. As far as I am concerned, a tester which 'detects/displays/confirms continuity' when the resistance is anything more than just 'a few ohms' is a potentially liability!

Kind Regards, John

 

[Iggifer]

Oh i see. Well yes, anything without a readout is dangerous. Even the best model in the range only displays it to a sensitivity of 1Ω with a +50%(!!) accuracy. Kind of pointless really.

 

[JohnW2]

Oh i see. Well yes, anything without a readout is dangerous. Even the best model in the range only displays it to a sensitivity of 1Ω with a +50%(!!) accuracy. Kind of pointless really.

Yes, that's the point. If I were using a device which (seemingly like the T50) gave just a yes/no indication of 'continuity' (i.e. something approaching a true 'continuity' test), rather than actually displaying resistance, I would expect it to answer 'no' if the resistance was greater than, say, about 10Ω. To report "Continuity=Yes" with even 100Ω, let alone 200,000Ω (if that's what the instructions means it does), would, IMO, be inappropriate and misleading/confusing.

Kind Regards, John

 

[ban-all-sheds]

There can always be faulty (relatively) high resistance joints, but really continuity testing is a "go/no-go" test where you are expecting either virtually 0Ω or ∞Ω.

Anything else is a resistance measurement.

Spoiler

Yes - I'm probably as guilty as all of us of saying "continuity testing" when I mean "resistance measurement"...

 

[JohnW2]

There can always be faulty (relatively) high resistance joints, but really continuity testing is a "go/no-go" test where you are expecting either virtually 0Ω or ∞Ω. ... Anything else is a resistance measurement.

Quite. As I implied before, in the real world one has to allow for a bit of resistance - which is why I suggested something like "<10Ω" to represent continuity. However, I would usually want anything above the chosen limit to be regarded as "no continuity", even if the resistance is nowhere near ∞Ω. As I said, if it is the case that this Fluke device will say "Continuity=Yes" with any resistance up to 200 kΩ, that strikes me as pretty ridiculous.

Yes - I'm probably as guilty as all of us of saying "continuity testing" when I mean "resistance measurement"...

As you know, I've a bit of a 'thing' about this, and certainly have not 'caught' that terminology off electricians! I feel very odd whenever I find myself typing "continuity testing" when I'm talking about a quantitative resistance measurement, and therefore nearly always remember to put the phrase in quotes!

Kind Regards, John

 

[EFLImpudence]

Other things unclear.

This is from the fluke 100 range:

Why the difference in upper limits between Resistance and Continuity?
Remember this is not a switchable device; it auto-detects and not all of the range has an lcd display just an led ladder..

Also, the accuracy is 'RN+50%'

 

[EFLImpudence]

Further to above. My mistake.

Actually the devices with resistance measurement (**) and lcd do have a button to press.

 

[JohnW2]

Other things unclear. ... This is from the fluke 100 range: ....

Hmmm - well, if it means what one might think it means, than 400 kΩ for 'continuity' is even worse (IMO, 'even more ridiculous')than 200 kΩ!

Why the difference in upper limits between Resistance and Continuity?
Remember this is not a switchable device; it auto-detects and not all of the range has an lcd display just an led ladder..

You tell me! Is 1,999Ω perhaps the highest quantitative figure that can be displayed on the LCD, after which one just has the LED ladder?

Also, the accuracy is 'RN+50%'

Whatever that might mean!!

Kind Regards, John

 

[EFLImpudence]

Did you see my second post - correction?

 

[JohnW2]

Further to above. My mistake. ... Actually the devices with resistance measurement (**) and lcd do have a button to press.

What happens when you 'press the button'? I see that 'Test Current' and 'Overvoltage Protection' also have "**" !

Kind Regards, John

 

[JohnW2]

Did you see my second post - correction?

I have seen it now (but not before I posted that previous reply) - but, as you'll see (from my subsequent post) I don't fully understand the 'correction'.

Kind Regards, John

 

[EFLImpudence]

What happens when you 'press the button'?

Bizarrely it stays on resistance measurement and display for twenty seconds.

I see that 'Test Current' and 'Overvoltage Protection' also have "**"

The ** relates to the models which include the resistance measurement facility and 'The 'Test Current' and 'Overvoltage Protection' apply when on resistance measurement.

 

[JohnW2]

What happens when you 'press the button'?

Bizarrely it stays on resistance measurement and display for twenty seconds.

Fair enough. Do I take it that this means that my previous suspicion is correct and that 1,999Ω is the highest resistance that the LCD can display?

I see that 'Test Current' and 'Overvoltage Protection' also have "**"

The ** relates to the models which include the resistance measurement facility and 'The 'Test Current' and 'Overvoltage Protection' apply when on resistance measurement.

Fair enough.

Do you have one of these? If so, are you in a position to determine, roughly, how high the resistance can be for the thing to still report "Continuity=Yes"? Is it really anything like as high as 400,000Ω ? (As I've said, from my viewpoint, even 40Ω would really be too high!).

Kind Regards, John