Digital Multimeter millamp to microamp range switching in a project - Page 1
Forum section: electronics / beginners

author: Veramacor
author_rank: Regular Contributor
timestamp: January 08, 2013, 01:27:24 pm
content: Hello,I have a microcontroller circuit that consumes power at different current ranges depending on the sleep state.When the circuit is fully 'awake', it will run about 30 milliamps. When asleep, It may run at 150 microamps or less.My problem is with getting my multimeter to range between milliamps and microamps without breaking the circuit.I have recently purchased a FLUKE 116 HVAC that does microamps fine. But that meter is only good for up to 600 microamps. Thus I cannot have the meter in line with the circuit as my circuit starts at 30 millamps! I do have a FLUKE 115 that will read down to 1 millamp, but I really am looking to cover the 1 microamp to 1 millamp range. My mistake in buy the FLUKE 116 HVAC. I may be returning it.I have tried the el-cheapo harbor freight model - (dont do it btw). I was able to get readings but not correct ones - junk.I did buy an extech ex330 this morning that has micro and milliamp ranges. This is similiar to the harbor freight model as the dial on the face has ma and ua range you have to manually switch in between the two.My question is this - how can I avoid breaking my circuit when switching from millamps to microamps when switching the range on the multimeter?Example:1) DMM is in circuit and starts out in the milliamp range and is on2) Circuit is powered on and default state is 30 milliamps - DMM reads 30 ma no problem3) Circuit enters sleep mode and ramps down to 150 microamps. DMM may read 000 ma.4) DMM is switched manually (via dial on face) from milliamp range to microamp range.5) Circuit is reset because #4 broke the circuit, and the circuit defaults back to 30ma. DMM cannot read 30ma because it is in microamp range mode and circuit is broken.Maybe a large capacitor to avoid the temporary loss of power because of the DMM mode switch? But I do not want to introduce a capacitor into the circuit.Any ideas on how to get around this?Thanks!

author: UPI
author_rank: Regular Contributor
timestamp: January 08, 2013, 01:46:59 pm
content: Short across the leads when switching current ranges.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 08, 2013, 01:49:16 pm
content: +1

author: Veramacor
author_rank: Regular Contributor
timestamp: January 08, 2013, 01:51:14 pm
content: Billiant!Thanks UPI. Alligator clips just became much more valuable

author: UPI
author_rank: Regular Contributor
timestamp: January 08, 2013, 01:52:28 pm
content: Quote from: Veramacor on January 08, 2013, 01:51:14 pmYes, I know.

author: deephaven
author_rank: Frequent Contributor
timestamp: January 08, 2013, 02:02:21 pm
content: Looks like you have a solution. What I thought of was to put a low value resistor in series with the supply and measure the voltage across it get the current.

author: w2aew
author_rank: Super Contributor
timestamp: January 08, 2013, 04:04:52 pm
content: One thing you may want to watch is the burden voltage in each range when measuring your circuit - it might be larger than you expect.