0
\$\begingroup\$

I rarely use my multimeter in current mode (I usually it in voltage mode), but here I did a measurement:

enter image description here

I understand that the current is probably 220 mA (thus 0.22) but what is the signification of 02.2 (see the 3rd picture)? Which unit is it using to write 02.2?

If the unit when used in 200mA mode is 1=100mA (which I could understand), why wouldn't it be 1=10mA in 20mA mode (then it should display 022. in 20mA mode)?

\$\endgroup\$
  • 2
    \$\begingroup\$ to me this looks like your multimeter is malfunctioning, or you can set the unit on a button not part of this photo. \$\endgroup\$ – Marcus Müller Oct 6 at 10:43
  • \$\begingroup\$ It is nearly new (proster xl830l, rather cheap), probably it's a design issue? It works very well except this (voltage continuity test etc) \$\endgroup\$ – Basj Oct 6 at 11:17
  • \$\begingroup\$ Is 220 mA or 22 mA more realistic for a 9V powered 1990 synthesiser (the classical Yamaha PSR / PSS that many families had) \$\endgroup\$ – Basj Oct 6 at 11:19
  • \$\begingroup\$ neither. The purpose of a measurement device is taking the guesswork out, so speculation isn't really useful. This thing show illogical values, so the current draw might be anything, don't get hung up on the digits you see. \$\endgroup\$ – Marcus Müller Oct 6 at 11:26
  • \$\begingroup\$ @MarcusMüller Thank you for your answer. In order to know how a correctly working 3-digit multimeter behaves: let's say it's 220mA. What should be written in 2m, 20m, 200m, 10A range? I guess it's ^^^^, ^^^^, 220., 0.22, is that right? And for 22mA, should it be ^^^^, 022., 022., 0.02, is that right? \$\endgroup\$ – Basj Oct 6 at 11:55
1
\$\begingroup\$

look at the number next to the pointer, if all the digit positions are filled that would be the maximum reading on the display.

the decimal marks the boundary between one thousand multiplier an the next, betweem mA ad uA or between A and mA

I understand that the current is probably 220 mA (thus 0.22) but what is the signification of 02.2 (see the 3rd picture)? Which unit is it using to write 02.2?

the readings are 0, 220uA 2.2mA 220mA

But most of them are probably wrong, be aware that only the 10A range uses the 10A socket, by turning the knob you can provoke different displays, but they are not useful measurments.

For a Yamaha synthesiser from 1990 operating from 9V DC, 220mA sounds reasonable, and assuming the leads are connected to "10A" and "common" it would be the correct reading.

\$\endgroup\$
  • \$\begingroup\$ only the 10A range uses the 10A socket, by turning the knob you can provoke different displays, but they are not useful measurments.: this is the answer indeed. I used the 10A socket on the multimeter. \$\endgroup\$ – Basj Oct 7 at 6:33
2
\$\begingroup\$

The internal digital meter inside the multimeter is a 200 mV (0 to 199.9 mV) meter module. We know this because it is standard, popular specification and because the dial's most sensitive range is 200 mV DC.

For current measurement the meter needs to switch in a shunt that will drop 200 mV at the specified range current. From Ohm's Law we can work out the likely shunt resistor values.

Table 1. Shunt values.

Range      Shunt resistor
   2 mA    100 Ω
  20 mA     10 Ω
 200 mA      1 Ω
2000 mA      0.1 Ω
  10 A       0.01 Ω (gives 100 mV)

The readings are a little strange. The decimal point (which is switched by one contact of the selector switch) is in the correct place for each range but the current readings suggest that something isn't switching and that it is reading 0.22 on all.

enter image description here

Figure 1. A multimeter PCB showing the range selector contacts. Image source: Dismantle-It.

If it's not under warranty then open it up and check the wiping contacts are clean and touching the PCB.

\$\endgroup\$
  • \$\begingroup\$ Thank you very much for your answer, I'll accept the other one because it explains how to read the decimal, etc. but both are excellent! \$\endgroup\$ – Basj Oct 7 at 6:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.