Micromod MOD: 1726F Output holder for MOD 30ML - Manual (Page 14)

Using The Output Holder With MOD 30ML
MOD 30ML Application
10
OUTPUT HOLDER COMPOUND THEORY OF OPERATION
When the instrument powers up the process value is read first followed by the Return and
Sense inputs. The expression block “OP_T_LGC” is executed next with a result that
becomes true when both the sense and run initialization inputs are true. The sense input
will always be true when an output holder card is present. The run initialization input is
true for only a moment when the instrument first powers up. The output of the expression
block is connected to the track command input of the PID block. For this brief moment
that the expression block output is true the PID block output will track the Return input
connected to its track source. The PID block uses this output value until told to change
based on automatic or manual manipulation. This PID output value is sent to the output
block causing the output blocks output current to be equal to that of the Output Holder
output.
The Return input block is set up to receive 1 to 5 milliamps. Its input conditioning block
converts this to 0 to 100 as engineering units that correspond to the PID block output.
The initial value of the Sense input block and its corresponding input conditioning block
are set to false. As well the output blocks initial value is also set to zero. This permits the
output holder card to maintain control of the field device until the controllers output is
synchronized to the output holders output.
The TL_ctrl” tune list permits front face changes of the P,I&D values.