| Products > Test Equipment |
| BM789 continuity behaviour |
| << < (7/10) > >> |
| tomwilkinson:
My BM789 Firmware 78910 exhibits this problem intermittently. |
| giosif:
Thanks to all of you who tested and reported here! For reference, my unit is running FW 78911. So, I don't believe the issue is firmware related. Could they be different HW revisions maybe? |
| s_n:
I don’t have a 789, but I’ve seen similar behaviour on other meters related to charging capacitors. I can reliably reproduce it by shorting a capacitor to discharge it, then measuring continuity across the capacitor. Measuring repeatedly will not trigger continuity again until the capacitor is discharged. I would assume that this behaviour is related to the continuity open circuit voltage and the speed of the continuity mode. |
| LuisBe:
--- Quote from: LuisBe on September 06, 2023, 05:34:01 pm ---About the short continuity beep on a Chinese Arduino board, it strikes me that my BM235 doesn't behave like that. Maybe it is because the BM789 is much more sensitive so the continuity function is better on bigger boards than a small Arduino board. My firmware version is 78912, you will see in the video after displaying it, it turns off (I don't know if it's normal operation but I think it's not a problem). https://youtube.com/shorts/BC1WUbZbf5E?feature=shared Greetings to all. LuisB --- End quote --- Here is what Brymen told me about the behaviour of BM235 and BM789: "BM235 or BM789 Continuity function outputs around 1.7V and 2.3V respectively to test. [...] BM235 continuity response time is around 15ms and can not catch its SHORT CIRCUIT moment. BM789 continuity response time is very fast and is less than 100μs. It can catch its SHORT CIRCUIT moment and truly reacts what it measures. BM789 is a professional meter. Its Continuity design is with much faster response than most of other meters to target for the professional applications of needing very short-time Continuity tests. If this user would like to have slower Continuity response, maybe he could try to use BM789 Diode function to test" |
| Electro Fan:
- Just as I was about to hit upload on this post, I saw LuisBe’s post – thanks for following up with Brymen, LuisBe. We can certainly add Brymen’s response to the mix – but per some thoughts below it might be interesting to confirm via further testing what is happening with respect to the “one probe continuity beep”. ---- FWIW, I think it’s too early to draw a firm conclusion about the test results being reported in this thread. Perhaps there is unit to unit variation caused by hardware or firmware among 789 units and/or other Bymen models and/or other non-Brymen DMM models. (And maybe what we are seeing is partially explained by differences in designed-in model to model response times.) But another theory (hypothesis?) is that what we are seeing in terms of differing test results from users is not necessarily unit to unit variation or model to model variation among the test equipment but something more like “DUT to DUT” variation in the sense that each “DUT” is really not just a different “Device” but a different “Environment.” To rewind, what users are reporting is that the 789 sometimes emits a beep when only one probe physically touches something – sometimes it’s a conductor in a circuit and sometimes it’s just a finger touch from a user. The interesting thing is that these seemingly random beeps happen with just one observed physical touch to one of the probes rather than both probes. Normally we expect continuity to be signaled to the user with a beep when a circuit is confirmed to have some current detected between the probes. Next, per s_n’s comment (s_n, welcome to the EEV forums btw), it does appear that the Brymen DMMs are behaving in a way that is generally associated with capacitors. So then the question becomes: what capacitor(s)? An external “DUT” capacitor or maybe an external “DUT environment”, ie a capacitive environment, or an internal capacitor or capacitive circuit within the DMM? Or possibly some combination of capacitance change is being detected by the probe(s) along with some capacitive behavior occurring within the DMM? At this point, the most interesting thing, IMO, is not even whether the change in capacitance is occurring due to an external condition (in the DUT or in the testing environment), or internally within the DMM but the fact that the change occurs when only one probe is physically touching something (at least in the sense of a normal DMM continuity test with 2 probes where a user applies both probes to a potential circuit). This is just a guess but it seems that the amount of charge we are seeing build up and dissipate is relatively small. Perhaps what we are seeing is test equipment (a DMM with two probes) that has a sensitivity that is on the threshold of detecting and reporting (via the “random beeps") some change that is lower than the change that normally occurs with a physical touch to both probes; instead what we are seeing is a change that is occurring with some amount of electrostatic charge such that when one probe is physically touched the physical touch is just enough to create a circuit when in fact the other probe is also participating in the circuit via an electrostatic charge or discharge. This would indicate some relatively small amount of capacitor-like activity is occurring somewhere. So, now we are back to what small change is occurring? It seems it’s a bit too early to say what is changing but it also seems that there should be some way to measure and observe the change. In the same way that we can charge and discharge a capacitor and see the results on an oscilloscope it seems that we should be able to observe and measure what is happening with the DMM “random beeps.” It might require more of a metrology level test setup in terms of both more sensitive (more resolved and more accurate) test equipment than we normally associate with DMM continuity tests but it doesn’t seem that such test equipment and testing technique/know-how is beyond the resources and know-how of at least some EEV members. In my limited experience I have come to appreciate for example how relatively subtle changes in temperature can change resistance measurements in a simple resistive test. Such changes are not noticeable (or generally even of interest) when measuring DUT resistance around 1 ohm but as resistance measurements reach levels on the order of 10 milliohms or less temperature changes of a few degrees C result in different resistance measurements. My guess is that something similarly subtle is happening in users’ test environments and therefore it is perhaps different environments that Brymen 789 users are detecting and reporting. Or maybe it really is differences in DMM’s (ie, unit to unit variation) that we are seeing – but it seems that we should be able to devise a test with enough resolution and accuracy that we can explain what is happening. This last point is sort of important for readers here as what this thread is about, I think, is not complaining but rather explaining (and learning). Net, net: My guess is that the “random” nature of the beeps should be explainable through better testing. We might be literally in the “noise” and this might not be a good use of some people’s time and energy but for anyone who wants to look further I think this might be a fun and educational project - to see if we can more definitively test and observe what is causing a seemingly one probe continuity beep (but is in fact a normal two probe beep). I’m guessing it’s something low level but something that can be tested, observed, measured and explained with better test equipment and better test technique/know-how. |
| Navigation |
| Message Index |
| Next page |
| Previous page |