Hi All,
For my work it is becoming more common for me to measure lower, and lower resistances. Megger has a really good manual on how to measure down to micro-ohms (for example to determine the quality of bus bar joints etc). I have found the 4-wire measurement to be very repeatable, and useful of course, and I understand that to measure very low resistances the appropriate test current should be selected for the range you want to measure. Megger indicates the following currents and their corresponding ranges:
I am often measuring connections that are around 1 m.Ohm to 10 m.Ohm so I always use 10A to measure. My question is though, why do we need increasingly high current to measure increasingly low resistances? I am guessing higher current's give better resolution for smaller resistances but this is not explained very well on the internet. Can anyone tell me exactly why resolution has anything to do with current?
For my work it is becoming more common for me to measure lower, and lower resistances. Megger has a really good manual on how to measure down to micro-ohms (for example to determine the quality of bus bar joints etc). I have found the 4-wire measurement to be very repeatable, and useful of course, and I understand that to measure very low resistances the appropriate test current should be selected for the range you want to measure. Megger indicates the following currents and their corresponding ranges:
- Ohm range, 1 Ampere
- Milli-ohm range, 10 Ampere
- Micro-ohm range, 100 Ampere
I am often measuring connections that are around 1 m.Ohm to 10 m.Ohm so I always use 10A to measure. My question is though, why do we need increasingly high current to measure increasingly low resistances? I am guessing higher current's give better resolution for smaller resistances but this is not explained very well on the internet. Can anyone tell me exactly why resolution has anything to do with current?