User Guide

Calibration Procedure

After differential adjustments have been made, the unit should be calibrated as follows:

1. Immerse the sensing bulb for about 10 minutes in any medium of known temperature.

2. Turn dial to setting corresponding to bulb temperature.

3. Turn calibration screw (see Figure-12) until the switch actuating points, as indicated by

the dial of the low stage switch, straddle the bulb temperature. For example, if differen-

tial of the switch is set at 2°F and bulb temperature is 70°F, the readings for “R” and “B”

switch action on the low stage switch would be 69°F and 71°F, respectively.

4. If thermostat calibration point is low, turn calibration screw slightly in a CCW direction.

If high, turn slightly in CW direction.

5. To check differential between stages:

a. Move dial well above calibration point.

b. Start turning dial slowly towards calibrating temperature until the low stage switch

just clicks (makes to “B”).

c. Record dial reading at this point.

d. Continue turning dial in same direction until the high stage switch clicks

(makes to “B”).

e. Record dial reading at this point.

f. The difference between the two recorded temperatures is the differential between

stages. For example, if the low and high stage switch just clicks (makes to “B”) at

71°F and 77°F, respectively, then the differential between stages is 6°F.

Figure-13 Part Identification of Two Stage Thermostats.

Dial

Dial Screw

Thermostat Arm

Tension Spring

Plunger Spring

Thermal Element

Switch Insulator

High Stage Switch

Positioning Plate

High Stage

Terminal Block

Low Stage Switch

Low Stage

Terminal Block

Switch Insulator