High precision resistors used for current sensing are usually low ohmic value devices suitable for four terminal connections. Two terminals, called “current terminals”, are connected to let the electrical current pass through the resistor and voltage drop VS is measured on the other two, called “sense” or “voltage drop” terminals. According to Ohm’s law, the sensed voltage drop VS divided by the known resistance RS gives the sensed current IS.

The accuracy of measurement depends on the stability of ohmic resistance RS between the nodes – points of connection of the sense leads. This arrangement, called “Kelvin connection,” reduces, especially for low ohmic resistance values, a measurement error due to the resistance of the lead wires and the solder joints as the sensing is performed inside the resistor, in or close to the active resistance foil.

Foil technology is best suited for manufacture of low values due to the superior’s stability compared to thick film or thin film technologies.

Based on its expertise in Stress Analysis and Precision Resistors of extremely low TCR, Vishay developed several proprietary technologies for production of high precision current sensing resistors.

The use of Z-Foil allows the achievement of very low TCR over wide temperature ranges. This is due to the inherent flatness of resistance versus temperature curve of resistors produced with Z-Foil. In the case of current sensors, the relevant temperature range must encompass both changes – due to changing ambient temperature and due to self-heating.

Vishay achieves a very high precision in current sensing by:
• Using Z-Foil for very low TCR (0.2 ppm/° C typical) over wide temperature ranges. Z-Foil also provides a PCR (Power Coefficient of Resistance) of 4 ppm/Watt typical.
• Applying proprietary methods of manufacturing precision 4-terminal resistors.
• Applying its expertise in stress analysis.
• Examples of high precision power current sensing Z-Foil resistors:
      Leaded: VHP4Z, VPR247Z, VFP4Z, VCS331Z, VCS332Z, VCS232Z, VPR220Z, VPR221Z
      SMD: VCS2516Z

Selector guide
High Precision Current Sensing
Datasheets (12)