DESCRIPTION
The INVALCO Model CTS-5025B is the latest version of the thermal expansion-type temperature controls. It is provided the two adjustments, 1) temperature setpoint control, and 2) a unique proportionality control. The temperature setpoint control permits the instrument to be set at any position from 0°F to 750°F.
The proportionality control allows the operator to set the temperature span desirable. The proportionality control is calibrated from 4°F to 60°F, which is the temperature change required to produce 3-15 psi output.
The principle difference between standard CTS-5025 and the CTS-5025B throttling control is in the addition of a rotatable seat adjustable from the control face. The orifice in the seat is drilled eccentrically so that rotating the seat moves the orifice with respect to the adjusting screw. This regulates the amount the orifice is opened per degree of temperature reduction.
PRINCIPLE OF OPERATION
This temperature controller utilizes the difference in thermal expansion oefficient of two materials to produce a mechanical motion. The simplified drawing (Figure 1) illustrates this principle. The sensing element of the controller is installed in the vessel. Temperature changes surrounding the element cause the following reactions:
1.The outer metal tube will expand on temperature increase or contract on temperature decrease. The change in length is proportional to the temperature change occurring.
2. The change in length of the inner rod which has a low expansion coefficient is negligible. However, since one end of it is attached to the outer metal tube, the inner rod moves as the outer tube length changes.
3. The opposite end of the inner rod pushes against and supports a floating link holding it concentric with a spring-loaded inner valve. With a temperature decrease, the inner rod applies pressure on the floating link, causing it to pivot around the adjacent fulcrum point which tilts the inner valve plug off its seat allowing the output signal to increase. The temperature adjust knob adjusts the setpoint by moving fulcrum point up or down.
4. When used with the standard head shown in Figure 2, an increase in temperature produces a decrease in output.
Figure 3 illustrates the direct-acting head which, by changing the air flow through the head, gives an increase in output with an increase in temperature.