Feature: Sensors
Figure 4: Sensitivity is doubled and noise has been completely cancelled, but non-linearity has not been corrected Te reduction of electrical noise in a signal cable with two or
more wires is therefore mainly based on subtracting the noise from one input to another, thus minimising or completely eliminating the noise. To perform the simulations in this article and observe the
results, a platinum Pt100 RTD was used as the sensor, and a sweep was performed on it from -200°C to 850°C. Te nominal resistance of the RTD is within the range of most resistive sensors, and has a very wide variation between the maximum and minimum values, which allows us to see the influence of the sensor value on the analysis. However, any resistive sensor can be used for the simulations.
Classic Wheatstone bridge connections Connection with compensated cable resistance Figure 1 shows a 3-wire RTD configuration in a Wheatstone bridge, which compensates for the resistance of the wires. Te following are the bridge equations to use:
Te denominator shows ΔRT + 2RL, which creates a
delinearisation and a small error caused by the cable resistance due to its length. Figure 2 shows the simulation results. Although the cable
resistance compensation is improved, a very large noise signal is produced. Note that the output signal is amplified tenfold, which considerably increases the noise signal.
Dual sensor noise-cancelled connection Undoubtedly, it is the Wheatstone bridge configuration that provides the greatest noise reduction; see Figure 3. This consists of two opposing sensors on different branches, connected by four wires. The noise cancellation level is complete, as seen in Figure 4. It also exhibits the delinearity of the bridge, plus the delinearity of the sensors themselves. In this case, the sensitivity is twice that of the previous 3-wire bridge configuration. It’s worth noting that to compensate for cable resistance,
a 50Ω trimmer resistor is added to each cable, which should be adjusted to make the total resistance 50Ω. This makes it easier to use this configuration with different cable lengths. In addition, for complete noise cancellation, resistors R1
and R3 must be of same value. The 50Ω trimmer resistors must also be set to the same value and placed one between wire U4 of RTD1 and ground, and the other between wire U3 of RTD2 and voltage source V3; see Figure 3. This is
18 June 2026
www.electronicsworld.co.uk
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