Multimeter: Difference between revisions

There are many cheap Multimeters (less than 25 Euros) - differently equipped with features. For many purposes a device for less than 10 Euros can be sufficient.

=== on/off selctor and auto-off ===

Most very cheap multimeters don't have an on/off switch but only a rotary selector which has one position for "off" and all other positions mean the meter is turned on and meausuring - draining power from the battery when forgotten. Better multimeters have at least a dedicated switch for on/off which saves all the work like "rotate to off when work is done" and "rotate back to voltage measurement when you need it again". While this is more convenient it still doesn't help if you forget to turn the meter off after work. The most convenient type of on/off mechanisms is an "auto off" feature. After a certain amount of time the meter simply turns off. Some meters also have a warning beep before the shut off. (and even better units have a switch which disables the auto off for measurements which have to run over hours).

Many Multimeters have a combined measurement for connectivity and diode check. When connected in forward direction current flows through the diode and a voltage (the forward voltage) is displayed. When connected in reverse direction the diode doesn't conduct which is indicated by the meter as "not conducting" (the same is displayed when nothing is connected to the probes). The diode check is also a useful feature to check the function of an LED. When connected in the forward direction a bright LED emits a tiny amount of light. While for red LEDs a voltage below 2V is sufficient, blue and white LEDs need above 3V to be tested. Many diode testers don't use more than 3V - so the meter will display the LED as not conducting in both directions and the LED will also not light up. Unfortunately this is often not indicated in the description of a multimeter - so you'd have to try that on your own.