Low-value resistors, the terminals of the resistance and temperature coefficient is often can not be ignored, the actual design should fully consider these factors, you can use the additional sampling terminals to directly measure the voltage across the metal materials. A four-terminal connectionwill allow measurement system actually uses resistance as R0, and the common connection of the resistance R0 +2 xRCu for example, 10 mm long 0.3 mm diameter copper wire will increase the resistance of RCu 2.4 mW, 4mm long 0.2mmthe wide 35mm thickness of the PCB lead the RCu resistance is 10mW.

A four-terminal connection will allow the measurement system actually uses resistance as R0, and the common connection resistance R0 +2 xRCu
   
These examples show that the defective resistor or wiring unreasonable will lead to very large errors, copper cable accounted for 24% of the total resistance of 10 milliohms terminal resistor, or even a very short 4mm PCB layout resistance doubled. resistance materials and copper terminals prior to soldering the combination of surface cleaning process can reduce the additional resistance of the terminal, but the TCR influence still exists.
   
Described instance, the proportion of copper as small as only 2% (24% compared to the previous example), TCR but never close to 0 increases to 80ppm / K. The low-value resistor such structure in the technology the document lists only the TCR of the alloy material itself is definitely not is of no value.

   
The four-terminal connection to the measurement system direct access to the signal from the sensing element of high reliability
   
Actually has such a low terminal resistance by the electron beam welding of copper - manganese, nickel and copper resistance, through the reasonable wiring can be used as a two-terminal resistance close to the performance of the four-terminal connection, but the design must pay attention to sampling the voltage of the signal the connection can not be directly connected to the sampling resistor current channel, if possible, preferably from the sampling resistor connected to the current terminal below and are designed to microstrip line.