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4194S Controllers
July 2018
The controller output signal will not return to zero pressure until decreasing process pressure passes the lower
switching point. When making adjustments as described in the following steps, keep in mind that:
D Changing the set point adjustment will move both switching points equally in the direction of adjustment.
D Changing the proportional band adjustment will widen or narrow the differential gap between the two switching
points by moving the position of the lower switching point.
Figure 3-3 shows the relationship between the percent of sensor range between switching points and the proportional
band setting on the controller. The following example illustrates how to use figure 3-3.
Example: The sensing element has a range of 30 psi. The lower switching point is to be set at 10 psi and the upper
switching point is to be set at 25 psi.
Proceed as follows:
D Divide the differential gap (the difference between the upper and lower switching points) by the sensing element
range. Multiply the result by 100 as shown in the following equation:
Differential Gap
Sensing Element Range
D Locate the 50 percent line on figure 3-3. Move along this line until you intersect the curve. Read the proportional
band setting on the left hand axis. For this example, the setting is approximately 35 percent.
Figure 3-3. Curve for Determining Proportional Band Setting
% SENSOR RANGE BETWEEN SWITCHING POINTS
A2853‐1
1. Using the curve in figure 3-3, determine the correct proportional band setting for the desired gap (expressed as a
percent of the input span) between the switching points.
2. Set the proportional band knob to the desired setting determined in step 1.
3. Adjust the set point to the desired upper switching point.
4. Increase the process differential pressure until the controller output signal switches from zero pressure to full
supply pressure.
5. Decrease the process differential pressure to the desired switching point at which the controller output signal
switches from full supply pressure to zero pressure.
16
15 psi
x 100 =
x 100 = 50%
30 psi
Instruction Manual
D200158X012
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