30 C.F.R. § 77.314 – Automatic temperature control instruments.

(a) Automatic temperature control instruments for thermal dryer system shall be of the recording type.
(b) Automatic temperature control instruments shall be locked or sealed to prevent tampering or unauthorized adjustment. These instruments shall not be set above the maximum allowable operating temperature.
(c) All dryer control instruments shall be inspected and calibrated at least once every 3 months and a record or certificate of accuracy, signed by a trained employee or by a servicing agent, shall be kept at the plant.