VPG – Latest video demonstrates low thermal EMF characteristics of foil resistors (Vishay Bulk Metal ® Foil Video)

Vishay Precision Group (VPG) has announced that its Vishay Foil Resistors division (VFR) has released a New video that demonstrates the thermal EMF characteristics of four resistor technologies: thin-film, thick-film, metal-strip, and Bulk Metal ® Foil.

The short video demonstrates how a slight temperature rise can introduce significant thermal EMF error voltages in the thin film, thick film, and metal strip resistors, but causes practically zero thermal EMF error in the Bulk Metal Foil resistor.

Electronic components, and resistors in particular, incorporate dissimilar metals in their construction. When one of the two junctions of dissimilar metals is heated, a voltage is generated between the two junctions. This is known as the Seebeck or thermocouple effect, and it occurs in resistors at the resistor’s two element / termination junctions. When heat is applied to either junction, the error voltage increase is directly proportional to the temperature increase. This is called thermal EMF, and it can be a very big problem in applications where it is necessary to make accurate, low-level circuit measurements.

Using a test that measures and compares the thermal EMF error of a resistor, in both magnitude and decay time, the demo video introduced today highlights the inherent low thermal EMF characteristics of VPG Bulk Metal Foil resistors. The test system used in this demonstration consists of a precision voltmeter, laptop, thermal EMF test fixture, and 50mohm 2512 current sensing resistors. The test is simplified so as to be easily reproducible by any technician in any lab with the least amount of commonly available equipment. A small amount of heat is applied to the resistors by simply touching them with a fingertip; no high-temperature equipment is required. As soon as heat is applied, the thin film, thick film, and metal strip devices start generating significant thermal EMF error voltages. The VPG Bulk Metal Foil resistor, however, shows little to no thermal error voltage.

In real-life use, the heat applied to a resistor would come from multiple possible sources such as adjacent components, heat distributed along the circuit board, and from unevenly distributed self-heating, all which would result in higher temperature rise and much greater thermal EMF voltages. Thus thermal EMF is an important consideration when selecting current sense resistors for low-level measurement applications, and VPG’s Bulk Metal Foil resistors are the devices of choice, says the company.

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