Every conductor used has electrical resistance (except superconductors). If a relatively small current flows through the conductor, this resistance is not a problem. According to the relationship U = I × R, there will be a certain voltage drop and power loss on the line, which will be manifested as heating according to the relationship P = I² × R. Because, in addition to the resistance, the capacity and inductance of the line are also applied, we speak of the impedance of the line.

When powering devices with consumption in tens or hundreds of Amperes, the voltage drop on the supply wires is so significant that it needs to be compensated. For example, with a line impedance of 0.01 Ω and a consumption of 100 A, the loss is 1 V.

zapojenie vodičov Sense The picture above shows the effect of voltage drop and power loss with the same line impedance, 100 mΩ, and a current of 1 and 10 A. You can also see the difference between the voltage supplied by the source and the actual voltage that reaches the load.


In the case of constant consumption, the simplest solution can be used and set a higher voltage on the source by measuring the actual voltage on the terminals of the consumer and setting the source to reach the required value under load.


In fact, most of the time the device consumption fluctuates and this solution cannot be used. Therefore, the sources have a built-in function of voltage drop compensation (line impedance compensation). The terminals are usually marked "Sense, S+ and S-" and if this function is used we talk about "Remote sense" - measurement at the remote end.

zapojenie svoriek Sense na zdroji SM800
The Sense input is generally high-impedance (above 10 kΩ) in order to load the circuit as little as possible. Always use shielded wires for connection, their cross-section can be minimal.

The same principle is also applied when measuring small resistance, here we compensate the resistance of the supply wires with a four-wire connection (Kelvin, 4w)


Detail of Sense terminals and connection for local voltage measurement Sense+ is connected to the output terminal of the positive pole, and Sense- is also connected to the negative pole.

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