TM 5-3895-374-24-1
GP470FA
APPENDIX C:
ON TIME CALCULATIONS AND EFFECTS OF TUNING PARAMETERS
The following examples illustrate the calculations preformed by the controller to determine output relay operation. Various
deviations, proportional bands and cycle times are used to show their effect on the control action.
EXAMPLE 1:
Dryer Draft
(PV) = -0.30" wc
Setpoint
(SP) = -0.20" wc
Transmitter Range
(RG) = 1.00" wc (0.00" to -1.00" wc)
Proportional Band
(PB) = 50%
Cycle Time
(CT) - 5 seconds
Since the measured draft is greater than the setpoint the deviation is a positive value and the controller will respond by
energizing Relay 1 in order to Close the exhaust damper. The on time of relay 1 is calculated as follows:
DEV =
(SP - PV)
=
-0.20") - (-0.30")
=
0.10"
DEV
Output
=
PB x RG
0.10
0.50 x 1.0
=
0.20 Displayed as OUT 70.0 (50 + 20)
On Time
=
:
CT x Output :
=
:
5 x 0.20 :
=
1.0 seconds
Relay 1 will be on for 1.0 seconds and off for 4.0 seconds.
(page 3-49)
