Emerson E2 operation manual Loop/Sequence Con Trol, Logical Combination, Control Cells

basic functions:

•LOGICAL COMBINATION: Up to four inputs may be combined using standard logical combina- tion methods (such as AND, OR, XOR, etc.) The result is the command output value, which can be used to operate a relay.

•BYPASS: The command output may be configured to be bypassed to a fixed value by a switch or but- ton press.

•ALARMING: Alarms and notices can be generated based on the command value of all the digital inputs of the cell, plus occupancy, and schedules.

11.12.5 Logical Combination

A Digital Sensor Control module has four inputs num- bered 1 through 4. The logical combination of the Digital Sensor Control modules follows one of the following strat- egies:

•FIRST - The first of the four digital inputs received will be used as the logical input value. This combi- nation first looks at input #1. If the value of this input is undefined, it looks for other valid inputs, starting with #2 and descending in numerical order to #4.

•SELECT - The sensor module reads an analog input, which provides a numerical value from 1 to 4. This number determines

•AND - The logical input value will be ON only when all sensor control inputs are ON. If one or more of them are OFF, then the logical input value will also be OFF.

•OR - The logical input value will be ON if one or more sensor control inputs are ON. If all of them are OFF, the logical input value will also be OFF.

•XOR - This combination strategy is exactly the same as OR, except when all sensor control inputs are ON, the logical input value will be OFF instead of ON.

•VOTE - If more than half of the sensor control inputs are ON, the logical input value will be ON. Otherwise, if 50% or less of the sensor control inputs are OFF, the logical input value will be OFF.

11.13Loop/Sequence Con-

trol

The Loop Sequence Control application’s main func- tion is to read the value of an analog input, compare the

value to a setpoint, and generate a single analog output value. This output value is represented in three different forms: a single analog value from 0% to 100%, up to eight digital stage outputs, and a digital pulse width modulation output.

The output value(s) are generated by a PID Control cell, which takes into account both the input’s instanta- neous value and its rate and direction of change. The PID Control algorithm is similar to the PID algorithm used by Pressure Control, except the Loop Sequence Control application is designed to be used in a wider array of applications.

11.13.1Layout of the Loop/ Sequence Control Application

There are two different types of cells in the Loop/ Sequence Control Application: control cells and output cells. The control cells have a part in determining the PID output percentage. The output cells convert this PID per- centage to staged digital and pulse width modulation acti- vations.

11.13.1.1 Control Cells

The five control cells in the Loop/Sequence Control application act as “steps” in determining the final PID per- centage.

Step 1: Select - The Select cell determines whether the occupied setpoint or the unoccupied setpoint will be used by the PID cell. This cell reads in values for both set- points, chooses the one to use based on the value of an Occupancy input, and sends the appropriate setpoint value to the next cell in line, the Setpt Float cell.

Step 2: Setpt Float - The Setpt Float cell allows alter- ation of the control setpoint provided by the Select cell based on comparison of a “float” input to a range of val- ues. The floating setpoint is then sent to the next cell in line, the PID Control cell.

Step 3: PID Control

This cell makes the PID percentage calculation based on the value of the setpoint (received from the Setpt Float cell) compared to the control input, which is fed directly into the PID Control cell. The resulting percentage is sent to the next cell in line, the Filter cell.

Step 4: Filter - The Filter cell limits the rate of change of the PID percentage over time, and is typically used to keep the PID cell from over-compensating when inputs change drastically. The filtered PID percentage is sent to the final control cell, the Override cell.

Step 5: Override - Once the PID percentage is figured, the Override cell provides for overrides of the PID per- centage. The Override cell, when activated by a user-initi- ated manual override, will block the PID percentage from

Loop/Sequence Control Software Overview • 11-39