| Products > Test Equipment |
| Hacking the Siglent SDM3055 Bench DMM |
| << < (18/35) > >> |
| Kleinstein:
Measuring the noise if the DMM is not that difficult. The main tool it the DMM itself. The first test is measuring the noise with a short at the input and than calculate the noise from the data. The second test needs a low noise external reference to measure a voltage at a significant part of the full scale. This gives the second noise case that includes the noise of the DMM internal reference and maybe some extra ADC parts. The 0.1 to 10 Hz noise would be approximated by getting data with 20 SPS and calculate the RMS value over some 10 seconds. Chances are one could use a slightly different sampling rate (e.g. 25 SPS) and thus a slightly different frequency range throughout the tests. For the reference a 7 V reference needs an extra stage to divide down the reference to the ADC level (e.g. 2.5 V maybe 3.5 V). This can add quite some uncertainty / drift. So it is questionable if it is worth using an highly stable LTZ1000 with a divider that adds quite some drift. The 20 V range would still use the front end divider that adds quite some drift and also some noise. For a 2.5 V reference there may be a simpler replacement with another 2.5 V ref chip. For the ADC, lower noise ADCs may need a lower impedance input signal. As far as I understood it, they use the internal gain for the low ranges (200 mV, current). So the new ADC also needs this option. So the change is not that simple. One may have to build a small separate PCB for the Reference and ADC - so first step towards building your own DMM. The input amplifier (buffer) may be limiting the noise performance. I would expect some AZ OP as a buffer - a compromise between noise and input bias. At least an AZ buffer should be sufficiently linear. |
| alexvg:
Some news : I'm working on an interface using a HTML/CSS rendering for a more scalable and flexible possibilities/features. It takes a very long time because the power of the main CPU is very limited: I need to do a high level of optimizations and remove some CSS features (who need too much process time/power). I don't know when the first alpha/beta version will be release, "probably" in 2-3 months. Hope you'll enjoy my work. |
| supperman:
Quick Questions.. As I'm considering a Siglent DMM: Why don't they integrate current flow over time to get Amp/H. Seems super easy.. to get them to measure total charge on a battery for instance. (all the data is there). Seems that I would need to log all the readings and then run it in Excel on a PC? Does the Siglent log both Voltage AND current over time? (or only one or the other using the PC software). @alexvg any thoughts on expanding the math to do integration math? Also, given the time you are spending on this.. why not just design a DMM? Siglent will never let you sell software for their device.. |
| BillB:
--- Quote from: supperman on November 26, 2019, 06:46:05 pm ---Quick Questions.. As I'm considering a Siglent DMM: Why don't they integrate current flow over time to get Amp/H. Seems super easy.. to get them to measure total charge on a battery for instance. (all the data is there). Seems that I would need to log all the readings and then run it in Excel on a PC? Does the Siglent log both Voltage AND current over time? (or only one or the other using the PC software). --- End quote --- Good question regarding integrating current. I don't believe the EasyDMM software supports dual measurement mode at all. For meters without a channel card option, it only performs a single measurement function. |
| alexvg:
Hi, sorry for the delay... This Siglent DMM only do a single a measurement at a time. Current/Voltage uses time slicing with a relay. I'm working on a solution to provide multiple length and simultaneous math integrations. |
| Navigation |
| Message Index |
| Next page |
| Previous page |