Brymen 869s DC offset issue when reading ACmV

[David Hess]

Maybe it's the colour.   However these days maybe even shining gold would be possible! On the other hand I have to admit that I like the yellow colour of the Fluke too, pity that Brymen chose the red. But it has some positive meaning in buddhist tradition if I remember right.

Fluke's yellow is protected IP.  That was something they sued Tektronix over causing Tektronix to change the color of their meter holsters to deep blue.

[AVGresponding]

Maybe it's the colour.   However these days maybe even shining gold would be possible! On the other hand I have to admit that I like the yellow colour of the Fluke too, pity that Brymen chose the red. But it has some positive meaning in buddhist tradition if I remember right.

Fluke's yellow is protected IP.  That was something they sued Tektronix over causing Tektronix to change the color of their meter holsters to deep blue.

All the more ironic that they both ended up getting bought by Danaher. And then split off into Fortive.

[NickKUK]

Hi,
I have query about this as I'm on the lookout for a 5digit DMM that can handle up to 1kV (tube amps, solid state and other general electronics). I'm thinking that the BM869 would suit this requirement but reading the mVac threads, I'm in doubt.

The scenario I specifically want is the ability to measure the top of a triode cascode (320Vdc+small Vac) or power output stage (400Vdc+ with a small mVac to large 100Vac waveform).

Short question - can the BM869 do that or not?

Now I could use a HV film cap and measure the AC, but would auto ranging Vdc up to 800Vdc with a 100-200Vac component work to measure the Vdc side with the BM869?

(I have a scope but I'm looking for DMM)

[2N3055]

Hi,
I have query about this as I'm on the lookout for a 5digit DMM that can handle up to 1kV (tube amps, solid state and other general electronics). I'm thinking that the BM869 would suit this requirement but reading the mVac threads, I'm in doubt.

The scenario I specifically want is the ability to measure the top of a triode cascode (320Vdc+small Vac) or power output stage (400Vdc+ with a small mVac to large 100Vac waveform).

Short question - can the BM869 do that or not?

Now I could use a HV film cap and measure the AC, but would auto ranging Vdc up to 800Vdc with a 100-200Vac component work to measure the Vdc side with the BM869?

(I have a scope but I'm looking for DMM)

Short version?

Only mV range is always DC coupled.

So measuring 4 mVAC  riding on 5V (or more) is a no go in mV mode. In mV mode any combination that produces more than +-500 mV P-P. is a no go.
Id you want to measure mV level AC ripple on top of 200V, you need to use capacitor, and will have to measure DC separately.

But if you are in V mode (AC, DC, AC+DC) all works fine. And you can easily measure 10VAC riding on 800V.

[NickKUK]

Short version?
Only mV range is always DC coupled.

So measuring 4 mVAC  riding on 5V (or more) is a no go in mV mode. In mV mode any combination that produces more than +-500 mV P-P. is a no go.
Id you want to measure mV level AC ripple on top of 200V, you need to use capacitor, and will have to measure DC separately.

But if you are in V mode (AC, DC, AC+DC) all works fine. And you can easily measure 10VAC riding on 800V.

Perfect (as perfect as any DMM can be!).

[Fungus]

But if you are in V mode (AC, DC, AC+DC) all works fine. And you can easily measure 10VAC riding on 800V.

And then zap the next component you touch using the 800V stored in the internal decoupling capacitor. 

[2N3055]

But if you are in V mode (AC, DC, AC+DC) all works fine. And you can easily measure 10VAC riding on 800V.

And then zap the next component you touch using the 800V stored in the internal decoupling capacitor. 

And how is that different than any DMM ever made that has AC mode..? And not in AC+DC mode...

[Fungus]

And how is that different than any DMM ever made that has AC mode..? And not in AC+DC mode...

Who said it was any different? I'm just making people aware.

Please relax... not everything is a personal attack.

[bdunham7]

And then zap the next component you touch using the 800V stored in the internal decoupling capacitor. 

Sure, if you leave the meter in the 1000VAC range and for some reason then immediately go and put the leads on some small, helpless ESD-sensitive CMOS IC....

[2N3055]

And how is that different than any DMM ever made that has AC mode..? And not in AC+DC mode...

Who said it was any different? I'm just making people aware.

Please relax... not everything is a personal attack.

Exactly. I agree with you on this 100%.
Just making people aware, and no, it is not personal attack.
I have absolutely no animosity towards you. Relax.
Friends ? 

[Kleinstein]

The AC coupling can do harm when charged to a high voltage. By nature it does not discharge very fast. If you are lucky there is some 10 M directly at the input side to ground and than maybe some 1.1 M as input impedance for the actual AC input. So discharge may take a few seconds. In some cases the resitor to ground at the input is missing and the charge can stay there longer.

It happend to me once with a scope. Look for ripple on to of +-150 V range supplies - because of the low volatage and relative low frequency with an 1:1 probe. The step from the +150 to -150 was than a bit too much for the scope input with specs for some 200 or 250 V peak. Chances are a charged capacitor of the scope or DMM could also damage sensitive parts - not just very sensitive ones.

[David Hess]

It happend to me once with a scope. Look for ripple on to of +-150 V range supplies - because of the low volatage and relative low frequency with an 1:1 probe. The step from the +150 to -150 was than a bit too much for the scope input with specs for some 200 or 250 V peak. Chances are a charged capacitor of the scope or DMM could also damage sensitive parts - not just very sensitive ones.

On the coupling switch, some older oscilloscopes use the Ground selection between between the AC and DC coupling options to precharge the AC coupling capacitor.  Very rarely they have a separate precharge position.

[NickKUK]

Just to follow up - I've had the Brymen 896s for a while now and it's great bit of kit. I like the leads have screw fitting for the little banana connectors too but also the plugs also fit my other HV probe kits with big croc clips so no fingers in shock range.

It's valid point on the cap discharge and it helps the inbuilt bleeds that take the B+ & B- plus the DMM back down to zero. Top of the all tube cascode + CCS (+320) to bottom (-320) means with 640Vdc in there I'm not sticking my fingers anywhere near it to reposition whilst in operation! By the time the system has bled down to preposition so has the DMM.