A temperature sensor for a cold reference junction of a thermocouple is provided that may be incorporated permanently or removeably in a releasable connector having a first connector part arranged to engage releasably with a second connector part in which the thermocouple conductors terminate, so forming a cold reference junction for the thermocouple. When the two parts of the connector are engaged, the temperature sensor of the present invention is able to sense the temperature in the vicinity of a cold reference junction in the connector. The temperature sensor may be provided by embedding one or more thermistors into a flexible disk or plate-like seal able to fit around the conductors of the first connector part such that the thermistors make electrical contact with selected conductors of the first connector part and thermal contact with the cold reference junction.