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| High current shunt - temperature drifts |
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| CosteC:
--- Quote from: Phil1977 on July 22, 2024, 09:28:04 am ---Can you feed the currents you want to compare through the same CT? --- End quote --- No. I am testing CTs. Or Rogowski Coils. Generally, I need to measure large current and its relation to "small current" or "small voltage". In practice those are two "small voltages" - voltage from shunt(s) or voltage output from integrator (rogowski coil) But I would like to hear more about your idea. Can you share? |
| Phil1977:
It´s just a very easy idea: A current clamp or CT physically sums up all the currents flowing through it´s port area. This can be used to enhance the measurement accuracy. If you e.g. want to compare two lines carrying around 100A then you need 1% of measurement accuracy to resolve a difference of 1A. If you direct both lines antiparallel through your current sensor, then you just read the current difference, so that a current difference of 1A with a 1% CT gives you a resolution of 10mA. If the ratio is not one to one but any reasonable rational number, you could also feed several windings through the CT - though of course 400A lines may be too thick for that. |
| Fungus:
--- Quote from: CosteC on July 21, 2024, 07:41:33 pm ---What is your recomendation for such measurements? --- End quote --- Bigger heatsinks on the shunt. Edit: I should probably say "better thermal management of..." - too many literal pedants around here. |
| tszaboo:
--- Quote from: CosteC on July 22, 2024, 11:54:50 am --- --- Quote from: Phil1977 on July 22, 2024, 09:28:04 am ---Can you feed the currents you want to compare through the same CT? --- End quote --- No. I am testing CTs. Or Rogowski Coils. Generally, I need to measure large current and its relation to "small current" or "small voltage". In practice those are two "small voltages" - voltage from shunt(s) or voltage output from integrator (rogowski coil) But I would like to hear more about your idea. Can you share? --- End quote --- You should just run the same wire through the DUT then several times, and reduce the current significantly. |
| CosteC:
--- Quote from: tszaboo on July 22, 2024, 01:43:06 pm --- --- Quote from: CosteC on July 22, 2024, 11:54:50 am --- --- Quote from: Phil1977 on July 22, 2024, 09:28:04 am ---Can you feed the currents you want to compare through the same CT? --- End quote --- No. I am testing CTs. Or Rogowski Coils. Generally, I need to measure large current and its relation to "small current" or "small voltage". In practice those are two "small voltages" - voltage from shunt(s) or voltage output from integrator (rogowski coil) But I would like to hear more about your idea. Can you share? --- End quote --- You should just run the same wire through the DUT then several times, and reduce the current significantly. --- End quote --- Not really practical. LV devices have small apertures, and current density will increase when putting more turns as insulation takes space for copper. For MV devices putting more turns is simply not possible. Putting more turns causes issues with conductor position location and external fields, particularly important for Rogowski coils. I know for sure some labs use special lock in amplifiers and moderate current levels, but it is outside my budget now. |
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