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Products => Test Equipment => Topic started by: ez24 on October 21, 2015, 06:39:08 am

Title: Uni-T UT20B multimeter square wave output test -- what is this ?
Post by: ez24 on October 21, 2015, 06:39:08 am
Uni-T UT20B 

From manual :

-----------------------
C.  Square Wave Output

Warning
To avoid damages to the Meter, do not allow output terminals to reach higher than 10V.

To measure square wave output proceed as follows:

1. Set the rotary switch to (square wave symbol)

2. Connect the test leads across with the object being measured.
The measured value shows on the display.

Note

The frequency is approx. 50Hz.

The output voltage range will be over 3Vpp when it is loaded 1M ?

When square wave output testing has been completed, disconnect the connection between the testing leads and the circuit under test.

--------------------------------------------------------------------------

What is this for ?  What object?  What is measured?  What units?

Would the voltage (from the 10 volt warning)  increase with a smaller load?

FYI Manual --> http://uni-trend.com/manual2/UT20B%20Eng%20Manual.pdf (http://uni-trend.com/manual2/UT20B%20Eng%20Manual.pdf)

thanks
Title: Re: Uni-T UT20B multimeter square wave output test -- what is this ?
Post by: GNU_Ninja on October 21, 2015, 07:34:39 am
It's a signal injector. http://www.electroschematics.com/9455/signal-injector-circuit/ (http://www.electroschematics.com/9455/signal-injector-circuit/)

As I recall, that particular meter can output a square wave that you can use to fault find the stages of a circuit (usually audio amplifier stages). Just google 'signal injector/tracer' and you'll find lots of examples.
Title: Re: Uni-T UT20B multimeter square wave output test -- what is this ?
Post by: ModemHead on October 21, 2015, 12:26:32 pm
Quote from: ez24 on October 21, 2015, 06:39:08 am
The frequency is approx. 50Hz.

This "feature" appears on some of the cheapie 830-style models.  I've never had one of these meters to confirm, but it sounds like it is just the LCD backplane signal, probably (hopefully?) buffered through a spare CMOS gate or something.
Title: Re: Uni-T UT20B multimeter square wave output test -- what is this ?
Post by: ez24 on October 21, 2015, 03:31:43 pm
Quote from: GNU_Ninja on October 21, 2015, 07:34:39 am
It's a signal injector. http://www.electroschematics.com/9455/signal-injector-circuit/ (http://www.electroschematics.com/9455/signal-injector-circuit/)

As I recall, that particular meter can output a square wave that you can use to fault find the stages of a circuit (usually audio amplifier stages). Just google 'signal injector/tracer' and you'll find lots of examples.

because of this statement
Quote
The measured value shows on the display.
that throws me.

My guess is that it is outputting a square wave and the amplitude is what shows on the display and is variable depending on the load.  Seems a dangerous test since the amplitude cannot be controlled.  Even the instructions say do not let it get over 10 volts with a 12 v battery?
Title: Re: Uni-T UT20B multimeter square wave output test -- what is this ?
Post by: GNU_Ninja on October 21, 2015, 03:46:02 pm
Try 'measuring' across some resistors with your meter set to square wave mode, see what you get. If you measure across a 1M resistor does it read 3 Vp-p?

BTW the manual does give further info on the square wave source: "Output approx. at 50Hz square wave. As a simple signal source with 47k? resistance output."  ::)
Title: Re: Uni-T UT20B multimeter square wave output test -- what is this ?
Post by: ez24 on October 21, 2015, 04:06:31 pm
Quote from: GNU_Ninja on October 21, 2015, 03:46:02 pm
Try 'measuring' across some resistors with your meter set to square wave mode, see what you get. If you measure across a 1M resistor does it read 3 Vp-p?

BTW the manual does give further info on the square wave source: "Output approx. at 50Hz square wave. As a simple signal source with 47k? resistance output."  ::)

If I get this meter I think I would set up a pot to have a variable output square wave.  I missed the addition info but that makes it more confusing.

thanks
Title: Re: Uni-T UT20B multimeter square wave output test -- what is this ?
Post by: GNU_Ninja on October 22, 2015, 08:54:39 am
Quote from: ez24 on October 21, 2015, 04:06:31 pm

If I get this meter I think I would set up a pot to have a variable output square wave.  I missed the addition info but that makes it more confusing.

thanks

Save your money and put it towards getting a better meter. The square wave output on this thing is just a gimmick. Check out some of Daves tutorials on selecting a decent budget multimeter  :)

All I want in a basic meter is:

True RMS
Autoranging
Volts
Amps
Ohms
Continuity
Hold, & Min/Max functions
Properly CAT III rated

For the record I use a Fluke 115  :-DMM
Title: Re: Uni-T UT20B multimeter square wave output test -- what is this ?
Post by: ez24 on October 22, 2015, 03:53:05 pm
Quote from: GNU_Ninja on October 22, 2015, 08:54:39 am

Save your money and put it towards getting a better meter. The square wave output on this thing is just a gimmick.

I am looking for the smallest multimeter - regardless to quality or features or price.
So far it looks like the Uni-T  -  sorry I forgot to say this - this model came from another post on the "smallest multimeter".  If within a week I cannot find a smaller one, then I will order the Uni-T, I was just wondering what the square wave was for and how to use it.  Being a gimmick makes the most sense  :-DD     thanks