Odd multimeter behaviour.

[rch]

I have a Uni-T UT33D multimeter, a "free gift" with an order from an instrument distributor.  It shows odd behaviour on the AC voltage ranges, and I just wondered if I should be looking for a fault, or whether it is just as likely to be a design error.   I realise it is not an enormously valuable item, and I don't want to waste time looking at it if there is nothing to repair.

What happens is on the AC volts range a small positive voltage gives a reading of about 1.8 times it's value.  A negative voltage gives no reading.  AC voltages around 50Hz are correct in the absence of DC.

Does this sound like a fault?

[Ian.M]

It sounds like its AC range uses a half-wave rectifier.  Cheap & nasty s--t.

[ModemHead]

It sounds like its AC range uses a half-wave rectifier.  Cheap & nasty s--t.

Yep.  If a multimeter has two AC ranges, lowest one being 200V, you can pretty much count on it being just like any other 830 cheap-o under the hood.  No matter how pretty the plastic shell is.

[rch]

OK, thanks.  So perhaps the simplest thing is to just confine its use to simple voltage present/absent readings and continuity testing - or just throw it away!

[electr_peter]

Cheap meters measure AC voltage via diode. This means DC voltage show ~2 times the value in AC voltage mode (or zero AC volts in another DC orientation). It may be half-reasonable if you are desperate and know in advance what you measuring, but this situation rarely exist in the real world.

I suggest getting a better meter.

[rch]

Cheap meters measure AC voltage via diode. This means DC voltage show ~2 times the value in AC voltage mode (or zero AC volts in another DC orientation). It may be half-reasonable if you are desperate and know in advance what you measuring, but this situation rarely exist in the real world.

I suggest getting a better meter.

I've got a better meter - but the question is what to do with this one.  Generally speaking I don't think you can have too many, indicating different points in a circuit or for use when one fails.

[electr_peter]

Uni-T UT33D can still be used to measure (low level) DC voltages and resistance, so it is useful around cars or DC batteries. Just keep in mind that AC performance is pretty poor.

[rch]

Uni-T UT33D can still be used to measure (low level) DC voltages and resistance, so it is useful around cars or DC batteries. Just keep in mind that AC performance is pretty poor.

Thanks.  That makes sense. At least you all have reassured me it doesn''t need fixing!