Coffee Cup Warmer with Thermostat Control

This design represents a simple automotive (12V) coffee cup warmer, with digital thermostat. It is not meant to be a practical design, but rather to show some of the capabilities of modeling multi-discipline electro-thermal systems in SystemVision Cloud.

The design includes a "plant" model with both static and dynamic thermal aspects, including a tungsten heater element, conduction and radiation heat transfer, and heat capacitance. A "graphical" model of the temperature sensor includes math function-blocks to set the bandwidth (LPF), gain (sensitivity), offset bias and output voltage limiting. It also includes an output resistance.

The closed loop performance of the system depends on the sensor bandwidth and the sampling rate. Try using 1 Hz instead of 0.1 Hz for the pole frequency "FP" in LPF1, and a 0.2 second period for the sample clock. You'll notice that the faster sensor and sampling greatly improves the temperature regulation.

The thermostat includes a simple amplifier and a single-bit voltage-to-digital converter, with a threshold level that specifies the temperature regulation set-point. A digital clock and D flip-flop sample and preserve the desired state of the heater switch during each clock cycle.

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Mike Donnelly

Joined November 8, 2013
Design added Friday, August 26, 2016 | 9:12 am PDT