Emerson Fisher 4194S, Instruction Manual

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Instruction Manual
D200158X012
4194S Controllers
July 2018
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6. Narrow the proportional band slowly until the output signal switches from zero pressure to full supply pressure.
7. Repeat steps 4 through 6 until the controller output switches at the desired points.
8. Observe the process pointer when the output switches at the upper switching point. The process pointer indication
should be within
±
2 percent of the set point indication. If the output does not snap within
±
2 percent of set point,
refer to the calibration procedures.
Reverse‐Acting Controllers
The controller output signal will switch from zero pressure to full supply pressure when decreasing process pressure
passes the lower switching point.
The controller output signal will not return to zero pressure until increasing process pressure passes the upper
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 upper 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
x 100 =
15 psi
30 psi
x 100 = 50%
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.
1. Using the curve in figure 3-3, determine the correct proportional band setting for the desired gap (expressed as a
percent of the maximum input element 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 lower switching point.
4. Carefully adjust the process differential pressure to 100 percent of scale range. Then, decrease the process
differential pressure until the controller output signal switches from zero pressure to full supply pressure.
5. Increase the process differential pressure to the desired switching point at which the controller output signal
switches from full supply pressure to zero pressure.
6. Widen the proportional band slowly until the output signal switches from zero pressure to full supply pressure.
7. Repeat steps 4 through 6 until the controller output switches at desired points.
8. Observe the process pointer when the output switches at the lower switching points. The process pointer indication
should be within
±
2 percent of the set point indication. If the output does not snap within
±
2 percent of set point,
refer to the calibration procedures.
Principle of Operation
Overall Operation
Refer to the schematic diagram in figure 3-4.