Vishay Precision Group (VPG) has announced that its Vishay Foil Resistors brand (VFR) has released a new video that compares the accuracy of precision thin film resistors with the new generation of VFR COTS (commercial off-the-shelf) resistors based on Z1-Foil technology. Using the example of a circuit built around Intersil’s ISL28617 precision instrumentation amplifier, the short video shows how an increase in ambient temperature causes a TCR mismatch in the thin film resistors (TCR of 5 ppm/C), resulting in an error in the output of the amplifier circuit while having no effect on the Bulk Metal Foil resistor.
Using a precision weigh scale constructed with a Tedea-Huntleigh load cell and Micro-Measurements strain gages – both VPG products – and Intersil’s ISL28617 instrumentation amplifier, the video highlights the accuracy and stability of VFR’s FRSM Z1-Foil chip resistors under increasing ambient temperatures. In the demonstration, the scale is used to weigh gold at +25C and + 60C, first utilizing thin film technology for the gain resistors and then using the FRSM foil resistors, says the company.
At +25C, both the thin film and FRSM resistors measure 200 grams of gold for a value of $11,400. With an ambient temperature increase to +60 °C, however, the assembly utilizing precision thin film resistors weighs the gold as 197.8 grams for a value of $11,277 — which represents a “loss” of $123. The same assembly using FRSM foil resistors is not affected by the temperature change, providing an accurate measurement of 200 grams at +60 °C — and no loss in measured value.
“Increasingly, innovative semiconductor companies such as Intersil are recommending high precision VFR foil resistors as part of the reference designs for precision analog applications,” said Yuval Hernik, senior director of application engineering for Vishay Foil Resistors. “This is because precision amplifiers such as the ISL28617 depend upon the matching of gain resistors for accuracy. Changes in gain ratios due to thermal and environmental stress result in errors at the output, which, as the video shows, can lead to a significant and costly loss. Harmonic distortion is also a key feature when choosing resistors. High-precision Bulk Metal Foil resistors have less distortion for a given signal than other resistor technologies. For example, FRSM resistors offer a tolerance of 0.01% and a TCR of 0.2 ppm/C for exceptional gain accuracy. For circuits requiring a high degree of accuracy in every operating environment, the resistors provide unmatched stability through temperature excursions, load life, and extraordinary environmental stresses. For the ISL28617 and other precision amplifiers, the FRSM is the device of choice.”
