Test and Measurement Forum

hi, i brought the ADC 11 acquisition system to measure the fuel cell i constructed myself. i knew that the converter itself have an internal resistance of 2.5Mohm. According to the the guide, v can connect the fuel cell directly(without connecting to a load) to the terminal board connected to the converter, which used to measured open circuit potential.
to ensure that the recorded data was correct, i measured the same cell with my multimeter and i turnout to get a lower voltage value.
i don't know why? hope that you can help me.

Hi,
It all depends on the output resistance of your fuel-cell. Our ADC-11 has an input resistance of about 2Meg ohms. A standard DVM has an input resistance of the order of 10Meg ohms. That is enough to make a significant difference to the reading if you fuel-cell has an output resistance of 100K ohms or more. If you connect both at the same time, the readings should be much closer to each other but lower than either previous reading.
Regards,
PeterF.

dear peter,

thk u for your explanation. i has another question, the converter im using is ADC-11 (USB) it have eleven channels. i used two channels, sometimes i found out that when two or three channels are used together they interrupted each other n end up with zero value??? i dont noe y?

hope to hear from u soon. thk u.

regards
yona1437

Hi

What do you mean when you say that the channels interrupted each other?

Are you saying that you cannot use more than one channel?

Robin

Hi,

i mean when i used one channel to measure the data is ok but when i connect another another fuel cell to the second channel the first channel data drop to zero??

(the fuel cell anode was connected to channel and cathode was connected to ground. hope im not connect it wrongly.)

I would suggest testing the channels with a DC power supply first to confirm that there is not a problem with the ADC11.