to have microamp (uA) in a compact meter? - Page 1
Forum section: electronics / beginners

author: nomorebots
author_rank: Newbie
timestamp: September 23, 2015, 06:58:06 am
content: Hello there,I am designing a compact card type, on the go multimeter that is slightly larger than a deck of poker cards. It will include regular measurements such as mV, V, mA, A, ohm, continuity, Hz, Cap, Temp and so on. Would like to get some pointers about whether to include microamp function or not. Here are the considerations:1) How many times did you use uA in the last 3 months? And how important is it to include uA in the package? What accuracy do you need and what did you use it for? (assume uA can be a add on to the meter later, like the uCurrent GOLD from Dave Jones)2) include microamp (uA) will require 4 banana ports instead of three. This will make the meter larger. If all banana ports are 19mm (3/4in) spaced apart for standard spacing, the meter will be as wide as a regular 4 port meter (compare to a deck of poker cards that is easy to carry around). Maybe we can remove the standard spacing and put all sockets one next to each other. (not sure if this will b acceptable for safety testing) Any thoughts guys?3) say if adding uA will require putting in a fuse in which will effect end price, will you want to pay 10~15USD more on top of original price?Thanks.

author: jwm_
author_rank: Frequent Contributor
timestamp: September 23, 2015, 07:15:36 am
content: $10-15 more that $60 is a different beast than $10-15 more than $300. What is your expected unit cost?Can you do microamps well? as in, with a really low burden voltage a la uCurrent? If so, that would be super cool, if you can't do it particularly well, don't include it as a specialist tool like uCurrent would be needed anyway. Since you seem to be targeting people in the know, the quality of the features provided rather than the length of the bullet list of supported features is probably more important. (and yes, I do really enjoy my fluke 101)

author: Mr.B
author_rank: Unknown
timestamp: September 23, 2015, 07:29:13 am
content: Good on you for having a go at this.I have a Mooshimeter...https://moosh.im/mooshimeter/You will need to be better in either specification and/or price point... USD120

author: nomorebots
author_rank: Newbie
timestamp: September 23, 2015, 09:28:47 am
content: do you use uA on your meter? how stable is it?Thanks.

author: mikerj
author_rank: Super Contributor
timestamp: September 23, 2015, 01:55:24 pm
content: Quote from: nomorebots on September 23, 2015, 06:58:06 amSounds a bit like aUT120C

author: Kleinstein
author_rank: Super Contributor
timestamp: September 23, 2015, 04:46:03 pm
content: At very small size, you might not be able to get a resonable CAT rating anyway. It really depends on the way you build it wether you need an extra inut for the µA ranges. A switch from the mA ranges might be enough, and one might also use the same fuse.

author: Mr.B
author_rank: Unknown
timestamp: September 23, 2015, 07:34:13 pm
content: Quote from: nomorebots on September 23, 2015, 09:28:47 amYes I do.I purchased the device specifically for measuring the active and sleep currents of battery powered MCU projects.With these projects I can measure both battery voltage and current at the same time on one device.The benefit of the Moshimeter is its ability to log this data over time.The only downside is 2uA resolution, however this is good enough for what I need it for.The device is fairly stable, however I would have to do a deliberate test with it logging a constant current source to see just how stable it was.

author: JoeN
author_rank: Frequent Contributor
timestamp: September 24, 2015, 01:04:47 am
content: Maybe you want to have that function in the firmware but make it so you can optionally leave off those expensive parts on the build, that way you can have a few different models at different price points.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 24, 2015, 03:03:47 pm
content: It really depends what you are doing, if you need a µA range. Sometimes you don't miss it for years, and others might want it daily. Possible uses for µA ranges are checking leakage on larger Diode / MOSFETs and looking at the consumption of low power circuits.Often accuracy is usually not that important in such a small meter - still better to have a 20 µ range with 10% accurary than having to use the 2 mA range. With meters that have µA ranges - readings are usually stable. Things might get poor in ranges for less than 10 nA. There is allways the option to use a low voltage Range and an external shunt - in the extreme case the 10 M input impedance at 200 mV as a 20 nA range.