Instrumentation Calculators

# RTD Class A Tolerance Calculator

An RTD (Resistance Temperature Detector) is a highly accurate temperature sensor widely used in industrial applications. The accuracy of an RTD is defined by its tolerance class, with Class A being one of the most precise according to the DIN IEC 60751 standard.

This RTD Class A Tolerance Calculator helps you determine the permissible deviation in resistance for a specific temperature, ensuring your RTD measurements are within the defined accuracy limits.

1. Select the RTD Type: Choose the type of RTD configuration (2-wire, 3-wire, or 4-wire) used in your application.
2. Input the Temperature: Enter the temperature in degrees Celsius (°C) at which you need to calculate the tolerance.
3. Calculate the Tolerance: The calculator will provide the Class A tolerance value according to the DIN IEC 60751 standard, giving you the acceptable range for the RTD’s resistance at the given temperature.

The tolerance of a Class A RTD is a measure of its accuracy at a given temperature. This tolerance is most precise at 0°C and changes as the temperature increases or decreases. The tolerance for a Class A RTD is calculated using the following equation:

The Class A tolerance according to the DIN IEC 60751 standard is calculated using the following formula:

Where:

• The temperature, T, is expressed in Celsius degrees.
• The absolute value |T| ensures that the tolerance calculation is correct for both positive and negative temperatures.

For an RTD operating at 150°C, the Class A tolerance is calculated as:

Tolerance = ± (0.15 + 0.002 × |T|) °C

Tolerance = ± 0.15 + (0.002 × 150) °C

Tolerance = ± (0.15 + 0.3) °C

Tolerance = ±  = 0.45°C

This means the RTD’s resistance can deviate by up to ±0.45°C from the actual temperature, and it will still be within Class A tolerance limits.

• Ensure accurate temperature measurements in critical industrial processes.
• Aid in the calibration and validation of temperature measurement instruments to maintain accuracy.
• Guarantee that your measurements comply with high-precision temperature measurement standards.
• The RTD Class A Tolerance Calculator based on the DIN IEC 60751 standard is an essential tool for engineers and technicians who require accurate temperature measurements.
• Designed to be accessible, making it easy for engineers and technicians to use, even with minimal technical expertise.
• Flexible tool supporting various RTD types (e.g., Pt100, Pt1000), catering to diverse applications.
• By using this calculator, you can be confident that your RTD readings meet the strict specifications necessary for high-precision applications.

The below table showing the Class A RTD tolerance values according to the DIN IEC 60751 standard. This table provides the permissible temperature deviation for different temperatures.

This table is useful for quickly determining the acceptable range of temperature deviations for a given RTD and ensuring that the measurements are within the specified Class A tolerance.

• The tolerance in °C is calculated using the formula: Tolerance = ±(0.15 + 0.002 × |T|) °C, where T is the temperature in degrees Celsius.
• The tolerance in ohms is specific to a Pt100 RTD, which has a nominal resistance of 100 ohms at 0°C.
• The resistance tolerance is derived from the temperature tolerance using the sensitivity of the Pt100 RTD, which is approximately 0.385 Ω/°C at 0°C.

Class A RTD offers higher accuracy with tighter tolerance (±0.15 + 0.0020 |t|)°C, ideal for precise temperature measurement in critical applications.

Class B RTD has a wider tolerance (±0.30 + 0.0050 |t|)°C, suitable for general industrial use where extreme precision is less critical.

The accuracy of a PT100 Class A RTD is ±(0.15 + 0.0020 × |t|)°C, where |t| is the temperature in °C. This ensures high precision, making Class A RTDs suitable for applications requiring precise temperature measurements.

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### Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe