| 摘要 |
<p>A temperature control system for cooling e.g. magnetic elements 14 in MRI apparatus, comprises a substance 16, a heater 26, a sensor 18 and a controller 20. In operation the substance 16 (e.g a wax or liquid) is held at its phase transition temperature (similar to the operating temperature of the elements 14) by the heater 26. The sensor 18 detects the change in phase and provides a signal to the controller 20 to switch off the heater 26. Heat may be removed from the wax via, a thermal sink 32. In an embodiment comprising wax, the sensor 18 may comprise a photodiode and an LED, on melting the wax becomes substantially transparent allowing the transmission of light through it. In an embodiment comprising a liquid the sensor 18 is a pressure sensing device, measuring the pressure of the gas boiled off the liquid by the heating of the magnets 14. Heating and cooling of the substance 16 may alternatively be achieved with a Peltier device.</p> |
