Multi-MCU Configuration Provides High-Reliability Temperature Readings

APPLICATIONS SUCH AS healthcare or aerospace systems require high reliability when making basic measurements. By using a microcontroller as the "master" to perform majority-logic voting of measurements performed by three small independent microcontrollers, this circuit design provides a high-reliability thermometer based on triplicated modular redundancy (TMR) (Fig. 1). The TMR scheme is able to tolerate the failure of one MCU or associated thermistor sensor to provide a correct temperature reading from 0 to 100°C with a resolution of 0.1°C, while the master MCU will discard the reading of the failed unit.

The reliability of each microcontroller module M is defined as:

R(t) = e^-λt (1)

where λ is the failure rate defined by the standard MIL-HBDK-217. Using the Reliability Analytics toolkit¹ , you can obtain λ for this specific device. The reliability for each PIC12F683 microcontroller in 1000 hours equals 0.9979 and is given by the formula:

R(t) = e^-2.152t (2)

The reliability for the voting microcontroller is 0.9978 in 1000 hours and is defined by:

R(t) = e^-2.228t (3)

while the total system reliability is given by:

where N is the number of modules, and M is the number of modules required...