12 replies to this topic

[dave]

does anyone know how to measure the current put out in the probes of a multimeter ?

 

just wondered if there was an easy mod that could limit the current output to 4mA or less so it could be used to check e-matches and total circuit resistance.

 

I don't actually need one but just curious ...as ever...........I guess this is more complicated than it seems

 

dave

[Arthur Brown]

Use another meter???

 

I have successfully used a cheapie craplin multimeter to check ematches. BUT for critical work a Blaster's safety Ohmmeter is the best option but they are about  £200+ each 

[dave]

I will try that Arthur, see what I get.
 
like you my meter can measure ematches without setting them off but would not like to depend on that.
the following site has a modified meter, which prompted me to wonder if the mod was relatively simple and do-able

http://www.blasterst...multimeter.aspx

[Arthur Brown]

Sorry but for $400 it would have to be more than just special to beat a cheap disposable craplin £10 meter. They used to supply a Blaster's safety ohmmeter but it seems to have gone from their listings.

[megabusa]

It will depend on the range selected. The higher the range, the less the short circuit current is available.

 

My DMM (Fluke 87) gives a max short cct current of 1mA on its lowest resistance range which falls to 0.5 uA on its highest range.

 

Not sure if you can actually measure it directly, I recall something about a calculation taking internal resistance & input impedance into account, but that was a long time ago & was probably with Avometers & not digital multimeters !

 

Will give it a try (as I have the spec for mine) & let you know.

Edited by megabusa, 29 May 2014 - 01:54 PM.

[Arthur Brown]

Swing needle meters tend to have much larger currents than digital meters..

[dave]

megabussa ....."My DMM (Fluke 87) gives a max short cct current of 1mA on its lowest resistance range which falls to 0.5 uA on its highest range".....

 

was this in the spec of the meter ? or did you measure it

 

dave

Edited by dave, 29 May 2014 - 07:48 PM.

[megabusa]

This is in the spec sheet from Fluke.

[pyrotrev]

I just checked a Rapid cheapy meter and it was 1.5mA on 200ohm range, 60uA on 2K range.

[dave]

pyrotrev,

 

I will be borrowing my sons multimeter this week

can you describe how you use one meter to measure the other

[megabusa]

Set your meter to the resistance range you are going to use.

 

Set your son's meter to the lowest current range.

 

Connect your meter probes to the other meter probes (doesn't matter which way it will just read +ve or -ve).

 

The value displayed on your son's meter will be the current given out by your meter.

 

It wont give the exact max output, due to internal resistance of the measuring (your son's) meter, but it will be pretty close. I would expect that the current through an ignitor will be less.

[dave]

good description,

 

thank you

 

dave

[dave]

made some measurements..

 

102 ohms......................................0.862mA

123 ...............................................0.875mA

200................................................0.839mA

300................................................0.815mA

850................................................0.225mA

1.1K..............................................0.209mA

10.13K..........................................0.022mA

 

I think my sons meter has an internal resistance of ~ 100ohms