| 摘要 |
<p>A heater for liquid has a glass tube (1) within which is disposed an electrically conducting heating coil (4). The heating coil is arranged to be an easy sliding fit inside the tube such that the majority of coil turns contact the inside of the tube at a plurality of locations spaced axially and peripherally of the tube. By such contact, heat is readily transferred from the coil to the tube and, thence, into a liquid in which the tube is to be mounted. The coil (4) may be bent into a U-shape and formed over an insulating member (5). An electrical circuit (fig 2) for the heater which avoids the use of a step-down transformer compares a reference voltage with the voltage across a thermistor (TH1) of the liquid and provides an output in dependence thereon to gate a thyristor (TR1), which when gated ON applies power to the heater. <IMAGE></p> |
