brymen BM869 nonconnected "settle" values - Page 1
Forum section: electronics / testgear

author: Redeeman
author_rank: Contributor
timestamp: July 16, 2015, 09:55:50 pm
content: Hello.I have just purchased a BM869s(elma rebrand in scandinavia), and i like it, but i am a bit unsure if something is wrong.If i simply take the leads put into COM and ohm/v/capacitance and put on table, spaced around 10 centimeters apart, and toggle through the different modes, it does not go to zero, and isnt fully "stable".I have gone through all settings and written down what happens, so perhaps someone can tell me if something is wrong or not. the probes are not touching eachother, or anything for that matter.here goes:first position:AC voltage mode:voltage: 5.xx to 0.1v over 10secHz mode:voltage: 3.xx to 000.1v over 5 secondssecond position:AC voltage mode:0.3xx - 0.08xxv over 10 secdBm mode:starts at 4dbM, goes to 2.3x over 5 secondshz mode:starts at 0.09xv goes to 0.083 in 5 secondsthird position:DC voltage mode:starts at 0.03xxx and very fast goes to -0.0000v, analog bargraph flipping the second "bar"AC + DC dual display modeAC voltage: 0.15x to 0.086v in 5 secondsDC voltage takes ~5-10 sec to go down to 0.001vAC+DC + AC dual display mode:AC starts at ~0.1 and goes to 0.86 over 5 secDC+AC starts at 0.51xx and quickly goes to 0.086xvfourth position:DC mv mode:starts at i think ~3mV quickly (1 sec) goes to 0.03mV, bargraph swings 3-4 bars a couple of times pr secondDC+AC dual mv mode:AC starts at 95.x mV and stays thereDC goes fast to 0.04mV and stays thereDC+AC + AC dual mode display:AC starts and stays at roughly 95-96mVDC+AC starts high, and inside of 1 sec jumps to ~94-95.xx mVHz mode:00.000HzD% mode:00.00fifth position:AC mV mode:HZ starts at 50.01Hz, stays thereAC starts at ~150.xxmV and within 1 sec goes to 92.xx mVHz/dbm mode:49.99hzstarts at 4dBm and within 1sec goes to 3.4xsixth position (temps):shows nothing on all modesseventh position:diod: 0Lcapacitance: 00.02nF, instant there, doesnt changeeighth position:ohms: autoranges down to .0L Mohm normally. same with beeperconductance: starts at 0.1x and swings around doing down to 0.01nS over a couple of secondsninth position:DC mV:starts at -00.001, jumps between -00.000. -23.99 to -25 % 4-20. seems properDC+AC mAAC starts at 00.01 mA, goes to 00.00 after a second or soDC starts at 00.000 and goes to 00.001 after a few seconds.DC+AC + ACAC starts at 00.00DC+AC starts at 6.4xx mA, after 10 seconds settles to 0.004mAAC:0.000Hz instantlyAC amperage starts and stays at 00.001mAtenth position:starts and zeroes down in at most 1 second on all modesThanks

author: rs20
author_rank: Super Contributor
timestamp: July 16, 2015, 10:10:07 pm
content: Why do you think something is wrong? It's a bit weird to just chuck a pile of numbers at us and expect us to guess what "looks wrong" about it.Anyway, I'm guessing you're expecting 0.00000V to be displayed on the DC volts ranges? Again, you should ask yourself why you expect that - if you short the probes together, that's 0V. If you leave the probes disconnected, there's nothing in particular defining the voltage across the probes, so the readout is undefined. The megaohm impedance of the multimeter itself will bring it close to zero, but not precisely so.In short: short your leads to test for 0V.

author: Redeeman
author_rank: Contributor
timestamp: July 16, 2015, 10:27:03 pm
content: thanks.the reason i was a bit unsure is that all the other (albeit much less precise and less featureful) meters i've had, fluctuated far far less with flying leads.I just retested with leads shorted, and it is not nearly like the numbers i posted, but it still takes several seconds to settle even after it settles scale, and on some of the AC/DC volt settings it never fully zeroes

author: dadler
author_rank: Unknown
timestamp: July 16, 2015, 10:29:49 pm
content: Is my Keithley broken too?http://youtu.be/2US974hVpkY

author: Redeeman
author_rank: Contributor
timestamp: July 16, 2015, 10:32:48 pm
content: I did not say it was broken, I said I did not know.

author: rs20
author_rank: Super Contributor
timestamp: July 16, 2015, 10:57:49 pm
content: Don't forget that the digits on the right hand side of your BM869 are down in the microvolts; it's not fair to compare them to the digits on the RHS of less precise meters.It is certainly possible that the BM869 is genuinely more noisy/unstable with open probe leads; but this is not a problem or fault at all.The readings you get on AC volts could well be genuine, a single turn of wire will pick up a certain amount of mains hum.

author: Redeeman
author_rank: Contributor
timestamp: July 17, 2015, 12:03:26 am
content: yes i was thinking that it might be because this is a much much more precise instrument than those $10 things i have been testing before, just wanted to make sureThank you

author: Lightages
author_rank: Unknown
timestamp: July 17, 2015, 01:42:15 am
content: Random number showing up on unconnected leads is to be expected. If you get random wild readings when connected to something, then I would worry.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: July 17, 2015, 03:51:53 am
content: Quote from: Redeeman on July 17, 2015, 12:03:26 amDon't forget, you have a high input impedance on your meter. When they are floating, stray fields can cause very minute currents to form. These minute currents across the high impedance give the fluctuating voltages that you see.