Ohmic Offset and Temperature Eco-efficiency
Nothing is perfect in this life, and that means that when it comes to measuring magnetic fields and voltages in the electronic world, plan B has to be put into action!
We know that the Hall Effect is all to do with measuring magnetic fields and movement, providing power and, again, movement in certain devices. While Hall Effect sensors, or transducers to give them a more formal name, are highly efficient and very high-tech, they aren’t perfect. For that reason, there are varying degrees that need to be taken into account when taking measurements. Overall however, these days the high quality sensors do give top quality measurements, it has to be said.
One of the key characteristics of a Hall Effect transducer is its level of ohmic offset, as well as its temperature co-efficiency. This might sound complicated, but like most things to do with electronics, it can be simplified down.
The problem basically arises when using a Hall Effect transducer on a bias current, e.g. a DC current. This means that DC voltage is applied between two very different points in the equipment, and that is done to control the flow of voltage through the circuit. DC is short for direct current. When using this type of voltage, a small voltage can sometimes appear on the output, and this happens even if there isn’t a magnetic field to be measured. This, of course, is not something that is wanted, but it can occasionally happen. This is all caused by something called ohmic offset.
Ohmic offset is when these changes in results occurs, but the lower the ohmic offset, obviously the better. The error can occur mainly when the contacts on the sensor are out of alignment, e.g. one is further up than the other. Ohmic offset is mainly expressed by output voltage.
If you are measuring a piece of equipment with a low magnetic field reading, it is best to have a Hall Effect sensor, or transducer, which has a high level of sensitivity, especially under those aforementioned DC conditions (bias). This is will obviously give you more accurate results, and a lower offset reading.
Another characteristic that we need to talk about is temperature coefficient of ohmic offset. These two work hand in hand, so they should be grouped together accordingly.
Sensitivity varies up and down, and so does temperature. When measuring using a Hall Effect transducer, the offset drift on temperature can often have no set pattern, whereas sensitivity can. Temperature offset is quite unpredictable and can cause issues. A highly sensitive Hall Effect transducer will therefore pick up on these changes and give you a more accurate reading, compared to a sensor which is less sensitive.
Overall, devices which have larger offsets, have higher levels of offset drifts. That might sound complicated, but basically, a piece of equipment with changes in temperature quite rapidly, will give you more ohmic offset, and therefore you need a more sensitive transducer to counteract the issue.
How can you counteract ohmic offsets drifts?
Aside from choosing a transducer which has a higher level of sensitivity, there are a few techniques you can use. Each transducer needs to be set for particular conditions, in order to give the best reading and results. This also means that you can see any offset issues in your readings, and counteract them as required.
While ohmic offset is a complicated subject, it is really only about a slight hitch in readings. This can be recognized by the fact that you are probably reading a DC bias current, and then you know to switch to the more sensitive version of your Hall Effect transducer.