So I'm about to buy a 6.5 digit multimeter.
I'm planning to use it for measuring highly efficient DC-DC converters in the following range:
Vin:40-120V
Vout:140V
Iin:0.5-7A
Iout:0.14-6A
Preferably I'd get a multimeter with an integrated multiplexer so i can measure all 4 values at the same time, but it seems like that doesn't exist in my ranges and I'd have to make an external multiplexer myself, I'd probably make a setup with 4 relais, 2 shunts and a nucleo board to control the relays using a comupter. (I don't have the budget for buying 4 bench multimeters btw) The external shunts might be inaccurate but this is ok becasue i can callibrate them against each other and find the relative error in resistance between both of them making my efficiency measurements accurate even though i have inaccurate specced shunts. In order to control the multiplexer and save the measurements I'd probably write a labview program.
I'd like to be able to have a resolution of 0.01%, and an accuracy of around 0.10% on the efficiency measurements, so desiring around 0.0025% resolution / 0.025% accuracy on each 4 of the individual measurements. So it seems reasonable to go for a 6.5 digit multimeter.
I'm now considering the following options (but open for other suggestions):
Siglent SDM3065X
fluke 8845A
And I'm having a really hard time deciding.
Seems like I'd have to use the 1000V range on the fluke for the voltage measurements, whereas the siglent has a 220V range giving an extra digit there.
for the current measurement I probably end up using a 10mOhm shunt and the 100mV range on the fluke, or a 20mOhm shunt and the 200mV range with the siglent.
So I went through the effort of calculating the worst case measurement errors on the overall efficiency measurement, taking into account the 4 measurements. I used the specified errors for 1 year after callibration and being within +/-5 degree from the calibration temperature. i made
this google sheetThan i got this:
Iin | 0.5A | 1A | 2A | 3A | 5A | 7A |
max error siglent | 0.159% | 0.090% | 0.056% | 0.044% | 0.035% | 0.031% |
max error fluke | 0.247% | 0.142% | 0.090% | 0.072% | 0.058% | 0.052% |
So the siglent seems to be slightly more accurate on paper, the inaccuracy at lower input voltages / currents seems to be slightly worse than what i desired, but i can deal with this, and even fix it by taking a larger shunt for those measurements.
I'm able to get the fluke for EUR1075 , the siglent for EUR820 including VAT.
So on paper the siglent seems more accurate, it has a nicer display and than it seems to be slightly cheaper.
But than pretty much everyone is telling me that they would probably go for the fluke because they are known to make really good multimeters.
So now I'm trying to see if anyone else here could give me some thoughts on this, or maybe there is someone that has experience using both multimeters and can share some of the experiences.
Thanks a lot