At Hemargroup, we are at the forefront of the design and manufacture of electronic components. With the new section HemarPills we want to share some of the best practices of our industry, to help simple electronics enthusiasts and companies, in the development of their projects.
In today's article we will see how to measure low-value resistances, a topic that is certainly interesting given the considerable difficulty.
Anyone who has used automatic test stations is aware of the difficulties in measuring resistances below a certain value.
There are cases where the resistive value of a component is much lower, even in the order of tenths, hundredths and thousandths of ohms, and sometimes you need to know that value. Components of this type are, for example, shunt resistors, high frequency antenna coils, electrical cables, metal tubes, special joints, resistors of water heaters and stoves and so on.
If we consider that the component under test is physically located several tens of centimeters from the measuring instrument, that the measurement "passes" through a contact nail, its receptacle, the wrap wire inside the adapter, at least a pair of DIN connectors and a few tens of centimeters of flat cable, we can say that throughout the connection chain we have a parasitic resistance between 1 and 3 ohms.
To overcome this situation we use the "4 terminal" measuring system, two wires pass the necessary current for measurement, the other two are connected to the measuring instrument, which, having a high input impedance, is not "disturbed" by the parasitic resistance of the connection. This results in an accurate measurement even on resistors with values below 1 Ohm.