Hi There,
I have been building a closed loop AC/DC current sensor, with the end goal to detect 500 mA of current at the full scale output. I have successfully designed circuits from 25A to 400A with acceptable error. The holy grail, though, is low-level current measurement, with a high degree of accuracy. It appears I have figured out much of the electronics, so this is more about the physics of the magnetic circuit, for which I am undoubtedly less skilled.
For a depiction of the high-level circuit I am talking about, see here: https://upload.wikimedia.org/wikipedia/commons/thumb/c/c4/Closed_loop_hall_effect_current_sensor.svg/431px-Closed_loop_hall_effect_current_sensor.svg.png.
At a sensor sensitivity of 5A, a problem emerges that I am hoping someone could help me with. The present configuration of the sensor is so sensitive that the measurement is notably disturbed by:
1) Bringing steel/ferrous objects near the sensor. I found that waving a pair of pliers in front of the core could cause the circuit to completely saturate (Vout >= Vmax)
2) Merely rotating the sensor 90 degrees (presumably into/out of the Earth's magnetic field) causes as much as 500mV of error in the quiescent offset voltage (Voq = Vout @ (Ip = 0A))!
Does anyone have any guidance on things to try?
1) The present magnetic core is made out of a ferrous (iron-based) material called "kool mu." That is: 85% Iron, 9% Silicon, and 6% Aluminum alloy. Would using a ferrite (NiZn or MnZn) reduce or eliminate the problem? Any other material suggestions? I'm not sure that this would, as any magnetic material would presumably respond undesirably, too, but I figured I'd ask.
2) Reducing the diameter of my magnetic core. Right now the inner diameter is 1.2". Should I expect lesser coupling to the external environment using a diameter of say, 0.8", or 0.5"?
3) reducing the ratio of primary to secondary turns. Right now I am at n = 1000. Presumably, reducing to n = 100 would reduce external, coupled magnetic fields by a factor of 10?
4) ???
Thanks in advance for any suggestions you may have!
Dave
I have been building a closed loop AC/DC current sensor, with the end goal to detect 500 mA of current at the full scale output. I have successfully designed circuits from 25A to 400A with acceptable error. The holy grail, though, is low-level current measurement, with a high degree of accuracy. It appears I have figured out much of the electronics, so this is more about the physics of the magnetic circuit, for which I am undoubtedly less skilled.
For a depiction of the high-level circuit I am talking about, see here: https://upload.wikimedia.org/wikipedia/commons/thumb/c/c4/Closed_loop_hall_effect_current_sensor.svg/431px-Closed_loop_hall_effect_current_sensor.svg.png.
At a sensor sensitivity of 5A, a problem emerges that I am hoping someone could help me with. The present configuration of the sensor is so sensitive that the measurement is notably disturbed by:
1) Bringing steel/ferrous objects near the sensor. I found that waving a pair of pliers in front of the core could cause the circuit to completely saturate (Vout >= Vmax)
2) Merely rotating the sensor 90 degrees (presumably into/out of the Earth's magnetic field) causes as much as 500mV of error in the quiescent offset voltage (Voq = Vout @ (Ip = 0A))!
Does anyone have any guidance on things to try?
1) The present magnetic core is made out of a ferrous (iron-based) material called "kool mu." That is: 85% Iron, 9% Silicon, and 6% Aluminum alloy. Would using a ferrite (NiZn or MnZn) reduce or eliminate the problem? Any other material suggestions? I'm not sure that this would, as any magnetic material would presumably respond undesirably, too, but I figured I'd ask.
2) Reducing the diameter of my magnetic core. Right now the inner diameter is 1.2". Should I expect lesser coupling to the external environment using a diameter of say, 0.8", or 0.5"?
3) reducing the ratio of primary to secondary turns. Right now I am at n = 1000. Presumably, reducing to n = 100 would reduce external, coupled magnetic fields by a factor of 10?
4) ???
Thanks in advance for any suggestions you may have!
Dave