# Platinum RTD sensor

*label*Science

*timer*Asked: Jul 1st, 2018

*account_balance_wallet*$10

**Question description**

A simple Platinum RTD temperature measurement system is to be designed to measure temperatures between 0 °C and 100 °C with a high accuracy. When supplied with a 10 V source voltage, the system produces an output ranging from 0 mV to 100 mV.

1. Design a bridge circuit for a Platinum RTD sensor. Using set values for bridge supply and output voltage, calculate the values of resistances R_{1}, R_{2}, R_{3}, R_{4}. Consider the effect of varying these resistance values e.g what happens to the system response if all four resistors are equal and if R3 and R4 are much larger/smaller than R1 and R2.

2. Calculate the current through the temperature sensor. How is this related to the power dissipation factor of the sensor?

3. The output from the sensor is to be fed into an A/D converter, which has an input range of 0 to 10V. If the sensor is placed in a remote location, select an appropriate type of amplifier for this system and justify your reasons for choosing the amplifier. Calculate the required gain.

## Tutor Answer

attached is the update of my answer

Question 1:

A bridge circuit for a Platinum RTD sensor can be designed as follow:

It is given that the circuit is supplied with a 10 V source voltage; therefore, Vs = 10 V .

Using the set values for bridge supply and output voltage, we have

VC = 60 mV

VD = 25 mV

And both of the above voltages of VC and VD are appropriate since they range between 0 mV

and 100 mV.

For the first series arm, ACB, we have

VC =

R2

Vs

R1 + R2

0.06 =

R2

10

R1 + R2

0.06 ( R1 + R2 ) = 10 R2

0.06 R1 = 9.94 R2

R1 =

9.94

R2 = 165.7 R2

0.06

For the second series arm, ADB, we have

VD =

R4

Vs

R3 + R4

0.025 =

R4

10

R3 + R4

0.025 ( R3 + R4 ) = 10 R4

...

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