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Digital Scale Image

Temperature Coefficient of Resistance, or TCR, refers to how the value of a resistor will vary with changes in temperature. This temperature change can be from changes in the environment around the resistor as well as the resistor heating itself as it dissipates power. There are a number of applications where minimizing the drift of a resistor over temperature is desirable. One such application are scales.

Scales may be used to measure the mass of gems, pharmaceuticals, or even larger items like construction equipment or bricks. Whether the scale is in a laboratory or located on a shop floor it is important that the instrument be accurate and consistent regardless of the environmental temperature. Most scales operate using the principal of a Wheatstone bridge as indicated in the image below.

diagram of a Wheatstone Bridge

In simple terms, the scale works by making one of the resistors variable due to mass. Anything other than a zero output means the bridge is out of balance. The magnitude of this imbalance can then be correlated to mass. Because the system relies on fixed ratios it is extremely important that the resistance values remain as stable as possible, since any variation could
potentially make the bridge unbalanced.

Riedon offers many low TCR resistor options, several of which are pictured below:

Riedon 100 and SM series image

Precision Wirewound
100, SM, 100PC series
• +/- 2ppm TCR
• 0.005% tolerance
• 1Ω to 9MΩ

Riedon SAA Series

Precision Thin Film
SCA / AA Series
• +/- 5ppm TCR
• 0.05% tolerance
• 10Ω to 1MΩ

Riedon CAR series

Precision Thin Film
CAR series
• +/- 1ppm TCR
• 0.01% tolerance
• 1Ω to 3MΩ

Riedon MF4200 series

Precision Network

MF4200 series
• +/- 5ppm TCR
• 0.1% tolerance
• 100Ω to 100KΩ

Article by Riedon Resistors

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