Instrumentation Calculators

RTD Calculator: Converting Process Temperature to measured Output Resistance

RTD Calculator: Converting Process Temperature to measured Output Resistance
  • In various industries, accurate temperature measurement is vital for ensuring product quality, safety, and efficiency.
  •  Resistance Temperature Detectors (RTDs) are widely used due to their reliability and precision.

Formula for calculation

One fundamental formula for estimating temperature based on RTD resistance is:

 RT = Rref[1 + α(T – Tref)]

In this formula, 

  • RT represents the output resistance of the RTD which you want to calculate at temperature T.
  • T is the measured process temperature.
  • Rref is the reference resistance at the reference temperature Tref
  • α denotes the temperature coefficient factor of the RTD,
  • Tref is the reference temperature of RTD

This equation establishes a connection between the RTD resistance, reference resistance (Rref), temperature coefficient (α), and reference temperature (T(ref). But let’s explore a different perspective: how can we deduce the measured resistance given the process temperature?

Example Calculation

Consider a scenario involving a PT100 RTD, characterized by the following parameters:

  • Rref = 100 ohms (resistance at reference temperature)
  • α = 0.00385 (typical for PT100 RTDs)
  • Tref = 0°C (reference temperature)
  • T = 50°C (process temperature)

The objective is to calculate the measured resistance (RT) using the formula  RT = Rref[1 + α(T – Tref)]

Here’s the step-by-step process:

Setting up the Formula

The formula links the measured resistance (RT) to the process temperature (T):

RT = Rref[1 + α(T – Tref)]

Substituting Known Values

 Insert the provided values into the formula:

RT =100[1+0.00385 X (50−0)]



RT=100 X 1.1925


At a process temperature of 50°C, the calculated measured resistance (RT) is 119.25 ohms, using the formula RT = Rref[1 + α(T – Tref)]

Key Considerations:

  • Linearity Assumption: The formula assumes a linear relationship between resistance and temperature, which might not hold over wide temperature ranges.
  • Reference Temperature: Accurate measurements depend on correctly identifying the reference temperature.
  • Accuracy Factors: Practical scenarios should account for factors like lead wire resistance and sensor accuracy.
  • The formula RT = Rref[1 + α(T – Tref)] is a versatile tool for estimating RTD resistance based on temperature. 
  • This example demonstrates its application in reverse: determining resistance from a known process temperature. 
  • Remember that while this formula offers a quick estimation, it’s essential to consider its limitations and potential inaccuracies, especially in non-linear or extreme temperature conditions.

RTD Calculator For Converting Process Temperature to Measured Resistance 

When an RTD is put in a process, the Process Temperature to Measured Resistance can be calculated with the help of the calculator that can be found below.

Ref the below link Converting Measured Resistance from the RTD to Process Temperature

RTD Calculator: Converting Measured Resistance to Process Temperature

Click here for more Instrumentation Calculators

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

Related Articles

Back to top button