Emerson Rosemount 56, Instruction Manual

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Section 7: PID Control Instruction Manual
April 2017 LIQ-MAN-56
62 Time Proportional Control
Transport Time Parameters: Basic Definitions
• Transport Time (On/Off) – Turns the Transport Time feature on or off.
• Transport Time (range 1 to 600 seconds) – When Transport Time is turned On; a
control appears at the right of it, which allows the value of the Transport Time to be
enter. This will be the time period that PID control output is held constant, while the
treated sample travels to the sensor.
• Run Time (range 0 to 60 seconds) – This is the time period that PID control action is
automatic. It always must be a shorter time than Transport Time.
Fault: Basic Definitions
1. Fault – When a measurement fault occurs (either sensor or transmitter) the control
output can be setup to continue providing a live control output or the output can be
set to a fixed value.
If the live reading is used during a fault condition, the control output could be based on
an erroneous measurement, which might cause problems. Using a fixed value for
control output during a fault condition can ensure that the control output goes to an
acceptable value.
2. Fault Current – If a fixed value on fault is chosen, this parameter selects the output.
The control output on fault can be set to a value to prevent a major upset or an unsafe
condition.
Note: If a fixed fault current output is chosen and PID control Mode is set to Manual, the
Manual output value will override the Fault Current value.