BM235 variability

[IanB]

Just a quick poll around anyone who has Dave's BM 235 and has tested the DC volt readings against a reference.

I have seen a few online reviews and on nearly all of them the meter when tested has indicated 5.000 V when tested against a 5 V reference. However my sample of the meter reads 4.997 V (about 3 counts low). I am fairly sure the reference is accurate from other tests so the meter seems to be off. Oddly the meter at 10 V seems to read spot on, so there is maybe a non-linearity at lower voltages.

What do other people see on their samples of the meter (if you have a known reference to compare against)?

I know 4.997 is within tolerance, but I am wondering how much variation there is between samples of the meter. Did I get an odd one out? Or did I break it by trying to power it with Energizer Lithium batteries?

[joeqsmith]

Just a quick poll around anyone who has Dave's BM 235 and has tested the DC volt readings against a reference.

I have seen a few online reviews and on nearly all of them the meter when tested has indicated 5.000 V when tested against a 5 V reference. However my sample of the meter reads 4.997 V (about 3 counts low). I am fairly sure the reference is accurate from other tests so the meter seems to be off. Oddly the meter at 10 V seems to read spot on, so there is maybe a non-linearity at lower voltages.

What do other people see on their samples of the meter (if you have a known reference to compare against)?

I know 4.997 is within tolerance, but I am wondering how much variation there is between samples of the meter. Did I get an odd one out? Or did I break it by trying to power it with Energizer Lithium batteries?

Did you watch Dave's video of them?

[joeqsmith]

Here's my BM235 compared with a few others including my old Fluke 97.  Keep in mind, the UT181 has been modified a fair amount after I damaged it.  The UT61E has also been modified.  The EX540, well it too was modified to the point where I had last changed out the RMS converter.   Then there is the UT90A which, while not modified, has been damaged more times than I care to count.  Then there's the BM869s which I also damaged and repaired.   The only untouched meter is the BM235! 

[IanB]

Seems like Dave had a few that read 4.997 V, but none lower than that. I guess I got an outlier. Bummer! 

[joeqsmith]

What's the uncertainty of your reference?  Is it NIST traceable and did you get the report with it?   

My old Fluke standard gets checked once in a great while against another meter which is kept in cal.  For home use, I never cal anything.  I did have my HP34401 cal'ed once with the report but that's been maybe 10 years ago.  Now days I check that box of resistors as well and keep records on them.  For time, I use the GPS.   Just wanting to be clear about the error in the pictures I show. 

I bought the HP34401 brand new from HP when it first came out.  It has never been aligned.  Here it is on the Fluke standard.  Of all the meters I showed earlier, this HP and my Fluke reference are what I trust. 

Also shown is my 5V home made reference. This thing is not in an oven and drifts a bit.  I use this as a quick check when looking at the meters I test but that's about all it's good for. 

 

[IanB]

What's the uncertainty of your reference?

I'd guess about 0.01%

Is it NIST traceable and did you get the report with it?

No, nothing so fancy 

However, as you can see from the attached picture, I do have reasonable agreement between three different meters.

[joeqsmith]

Yea, odd man out I would say.   

A little strange result but I let the old HP and Fluke sit for about a half hour and then recheck them together.  I then adjusted my test box against the HP.  The test box was then attached to the BM235A. 

Looks like they spec it to 0.3%+2d in the 6V range.  I have no idea if that's of reading or full scale, +/-0.3% of just +0.3%, Maybe +/-0.15%,  +2d or really +/-2d.  Some of these manuals leave a lot to the imagination.  Assuming +/-0.3% of 6V plus  +/-2mV.  That's a pretty wide window and we are both well within that.