Abstract: To test the soldering temperature on the upper surface of an electronic circuit ceramic substrate (16) that is conveyed on a moving belt (12) over a plurality of heater platens (10), a thermocouple (20) is yieldably pressed to the upper surface of the substrate by a pressing mechanism (22). The pressing mechanism (22) comprises two flat springs (54 and 56) that press an insulator (52) down onto the thermocouple (b 20). The flat springs (54 and 56) are in turn pressed toward the upper surface of the substrate (16) by a coil spring (62) which pushes down onto a pressure plate (60). The pre-load of the coil spring (62) is manually adjusted by a nut (64) that has a groove (66) around which the wire (24) of the thermocouple (20) is wrapped for strain relief, as the wire extends to a digital readout device (26) that rides on the belt (12) along with the substrate ( 16).