within 30 minutes after a temperature probe, initially at ambient temperature, is
inserted in the reference well.
(2) Stability. The ice point temperature in the reference well does not deviate
more than ƒ 0.03, Celcius from 0, Celcius over a 24 hour period of continuous
operation. The thermoelectric ice point is capable of reproducing the ice point
(0,C.) within ƒ 0.02, C when it is cycled through its freezing and thawing
(3) Service conditions. The equipment will operate satisfactorily under all of the
environmental conditions specified herein.
(4) Operational environment. The equipment can be operated after stabilizing
over the following range of environmental conditions:
(a) Temperature form 22, C. to 24, C.
(b) Relative humidity from 20% to 50%.
(c) Altitude from sea level to 10,000 feet.
c. THEORY OF OPERATION. The instrument maintains the reference well at 0,C
continuously. The reference temperature of 0,C is established by the physical
equilibrium of ice and water within the sealed reference cell. The ice-water equilibrium is
sustained by a thermoelectric cooler automatically controlled by a bellows-microswitch
sensing mechanism which responds to the relative volumes of ice and water coexisting in