| ??? 07/09/09 15:39 Read: times |
#166937 - spikes of source could be a problem Responding to: ???'s previous message |
Kai Klaas said:
What "bumps" can you tolerate? Less than 0.1%? What is the maximum allowed shunt impedance for each range? Are you allowed to have different shunts for different ranges? Are you allowed to switch the shunts during the measurement when changing the ranges? (You know that this can result in total desaster in combination with large inductances when doing the switchings wrong...) yes the bumps should be less than precision I need to measure. I have no restriction about maximum values, but higher values mean higher common mode voltage and more trouble and in higher current ranges it dissipates more. I have different shunts for different ranges, otherwise how could I measure 100uA to 10A with only one resistor? yes, I have to switch during measurement. Disaster, yes it is very evident when range changes but I have no inductive load fortunately. Kai Klaas said:
You say the current source is a constant current source. Does it produce glitches when changing the setting? Is there any need for protecting your circuit? (I once had to fight with a kV power supply which produced narrow kV spikes each time I changed the output voltage, even when I only wanted about 100V from it...) Very very good point!!! I never thought about that. I have to check it with oscilloscope to see if my current source actually produces such spikes when range changes. thanks for pointing it out. It can be the major problem but if it was the problem how should I eliminate it? should I modify current source or I have to remove it in firmware ? Kai Klaas said:
Why so many samples, when you have a constant current source? Why not using the dual-slope conversion technique like used in the ICL7106, e.g.? the current source produces ramps with different slopes, the slope may change suddenly so I have to record it with high sampling rate. |
