RIGOL Support fading out ? What is your experience ?

[rsjsouza]

... exactly. The schematics looks nice, but what they do is rip open the bridging relay before the connection to the multimeter current input (including the shunt) is established.
To me it looks like a beginners fault when programming the relay timing. Unfortunately, they refuse to work on this bug.

Wow, that is a pretty fundamental error which prevents usability.

[Wolfgang]

I did. They gave me a M302 model to continue my tests. This is a voltage/resistance only card with 20 channels. I made a shunt resistor to measure the current via the burden voltage. We still have to negotiate how to proceed, I still have the right to return it.

[Wolfgang]

... correct. I simply did not believe that they could be so silly. The M300 is on the market for a few years now .. 

[2N3055]

Regarding M300, if you want switching between different inputs, connected to different circuits, you HAVE TO break before make.. Or you will shortcut different circuits...
Only way to do it without breaking is to have several shunts, one for every input. On schematic, there is something that looks like a short link. Maybe place for shunt?
Or you could have duplicate relay, that will make a short IN1, than brake IN1, make IN2, unshort IN2....

But you have to break one input before make other, otherwise BOOM...

What scanner card from other manufacturer can do switching of current measurements, using meter internal current shunts and that doesn't break before make?
That would be interesting info..
Regards,

[Wolfgang]

... break before make for voltage inputs is fine and logical. The M300 always measures one channel fter the other, one by one.

For current channels it *should* work like this:
- leave input relay in bridge mode (see schematics)
- disconnect relay between input and meter for all current channels
- close connection from current channel to shunt inside meter
- open input relay and measure
- close input relay
- open connection from current channel to shunt inside meter

... next measurement.

If you are in autoscale mode, it would be OK if the lowest value shunt is tried first, but always with input shorted between shunt resistor changes, of course.

[2N3055]

... break before make for voltage inputs is fine and logical. The M300 always measures one channel fter the other, one by one.

For current channels it *should* work like this:
- leave input relay in bridge mode (see schematics)
- disconnect relay between input and meter for all current channels
- close connection from current channel to shunt inside meter
- open input relay and measure
- close input relay
- open connection from current channel to shunt inside meter

... next measurement.

If you are in autoscale mode, it would be OK if the lowest value shunt is tried first, but always with input shorted between shunt resistor changes, of course.

So shorting link in schematic is a separate relay? In that case it is second case I mentioned and it should be possible i that relay can be controlled separately.

[Wolfgang]

... I think the hardware is fine, only the programmers have no idea about electronic measurement practices 

Update 30.8.2018: RIGOL Germany agreed to pay me a decent measurement shunt because they could not fix the M300 problem. Although this is not optimal, I agreed to that. At least thats some support to get the customer out of a problem.

Lesson: Stay away from the MC3324 card, and ask RIGOL for a free shunt in case you need to measure currents with the normal MC3120 voltage card. This one seems to work nicely.

[TurboTom]

... exactly. The schematics looks nice, but what they do is rip open the bridging relay before the connection to the multimeter current input (including the shunt) is established.
To me it looks like a beginners fault when programming the relay timing. Unfortunately, they refuse to work on this bug.

I've got the same combination running here and since I'm rewiring a setup currently, I used the opportunity to do some testing to try to replicate your findings. My firmware versions of the relevant components are:

M300 (Mainframe) - 00.02.00.08.00
MC3065 (DMM) - 06.01.01.25
MC3324 (MPX) - 00.01.01.03

Setup: Initially I routed the current to be measured (70V PSU connected to a 68k resistor ...because it was just lying around on my desk...) connected to a single current channel (first and second screenshot), and connected in series to all four current channels (third screenshot).  I initially configured the acquisition system to scan alternatingly the current channel and a voltage channel (either on the same module or on a different one, this wouldn't make any difference). For the second configuration, I scanned the four current channels in sequence, then a digital port (that isn't related to the DMM module at all) and finally a voltage channel. This scheme relates to the third screenshot.

Findings: With only the first current channel connected, I didn't find any problems or interruptions of the current flow, whatsoever. Some ringing could be observed (probably when the DMM is disconnected and reconnected from/to the current measurement multiplexer) and the voltage drop across the shunt (100mOhm @ 2mA range) is present during the current measurement. The modified setup revealed more interesting details: While switching between the current channels, everything's fine again (some ringing present but it decays in a few hundred nanoseconds, and some picked-up noise due to the unshielded wires). But after current channel 4 had been read and the instrument reconfigures to voltage measurement, I get a clamped glitch (with some contact bounce) of 400µs.

My interpretation is the following: The multiplexer card is working correctly but the input configuration relay on the DMM changes state too quickly. There should be introduced a small pause before the DMM is reconfigured after measuring currents. Unfortunately, at least from the panel of the instrument itself, it's not possible to insert a "slot" with a "pause" in the acquisition list that just disconnects the current inputs (and hence shorts them) so only in the next step, the input of the DMM will be reconfigured. If this is possible via the "UltraAcquire" software, I didn't check. One possible and simple solution in case not all current measurement channels are in use would be to "dummy"scan an unused channel before changing over to voltage measurement mode. I also found that the current measurement channels appear to be clamped via two silicon junctions in series (shorted bridge rectifier?) so the voltage drop, even if the switching sequence is troublesome/faulty, should never exceed 1.4 volts. If this is a problem for the external circuitry depends on the particular configuration. Evaluating 4~20mA sensors should be okay.

Cheers -

[Wolfgang]

Thanks a lot for your tests. They look very plausible to me. Its a timing problem, but I found no way to adjust this using the M300 itself.

The latest state of affairs is that they took the current measurement card back, they sold me an M302 package for a reduced price, and they paid for a measurement shunt I bought from SEFRAM. So, it works now, but I dont have the combined card anymore so I can try out things.

After saying that they had no resources to attack this problem, they (RIGOL Germany) now said that they will follow up this eventually, but with low priority.

I (did not try this yet) foresee another problem with the current channels: If they are in autorange mode, the DMM must try high currents first and then step down to the lower current ranges. All this should be done with the current channel never opened, but always bridged out while the range switching occurs.

[vishaldotgupta]

Recently i have a had a chance to repair few Rigol equipment such as Spectrum Analyser and Sig Gen.  the support information available is too scarce.  A so called service manual available on their website hardly contains any useful information.

They do have wonderful products and at good prices but support information is hardly availalbe.  on the board level they resort to mask the part no of critical parts by laser etching etc.

This is never seen on other reputed global brands.  Are test equipments so easy to copy? and does laser masking can deter reverse engineering team?  it can only delay process but not stop it

[vishaldotgupta]

i am in need of flash memory dump for Rigol DS3060 or maybe complete motherboard

Rigol has already discontinued so its not available with them.