# Current measurement maximum time

On my multimeter I have two current measurement connection. One for the mA and one for the A. On the ampere one there's a time limitation but not on the mA one. Also they mention in the manual a kind of "cooldown time" after the measurement for the A one. So, basicaly, probing with this input can really slow down my project. (max 15 sec every 5 minutes)

My question is, I have to switch to that A one for a 600-700mA current (mA input is 500mA), as it's not a "big" current, can I bypass this limitation ? Is it design for higher current only or any measurement done on that input ? It's a middle-end multimeter but even the online datasheet is not complete about what. (Was excepting a kind of measured current/cooldown time graph)

• I haven't heard of that limitation being placed on any of the meters (handheld fluke 87 and keithley 2000) I've owned. Chances are, you'll be fine -- maybe decreased accuracy. How should we know without a datasheet or product link? – HL-SDK Dec 2 '13 at 3:32
• If you insist on doing it as quickly as possible, getting your own shunt and measuring the voltage across it will let you monitor the shunt temperature easily. But 700mA doesn't sound like an excessive amount of current; they're probably talking about 2A and up. – Ignacio Vazquez-Abrams Dec 2 '13 at 3:46

A typical multimeter manual would say something like this:

Function Overload Protection               Overload
mA       Fused, 440 mA, 1000 V FAST Fuse   600 mA overload for 2 minutes maximum,
10  minutes rest.
A        Fused, 11 A, 1000 V FAST Fuse     20 A overload for 30 seconds maximum,
10  minutes rest.


(example from Fluke 77-IV manual)

I guess the exact time allowed and rest time depend on the exact current and on environmental conditions too (ambient temperature etc). I've not seen more detailed information in any multimeter manual.

Multimeters are not really intended to be a permanent part of a high-current circuit.

• +1 for actual information rather than speculation. It may be that the "rest" requirement applies only to cases where you intentionally overload the meter, so that the fuses aren't blown. – Joe Hass Dec 2 '13 at 12:01
• I've read again the manual but this time the french part and no the chinglish part and apparently there's some informations the chinglish translator wasn't considering really important. In the french part there's a point saygin that it's indeed 10A 15sec max, 5minutes rest. I'll send a mail to the manufacturer to point the issue (who knows) but also ask if they have some kind of graph for that and check if I have to wait 5 minutes between each measurements of 700mA... – Emmanuel Istace Dec 2 '13 at 17:55

For a current less than 1A, as long as you don't let it run continuously through the multimeter (and probably even then), you shouldn't run into any problems with frying components.

The problem with large currents is the large power dissipation in the shunt resistor, so it heats up. Thus, the specified duty cycle for measuring large currents.

I hope that helps.