30 November 1998
Set full-stroke travel of actuators matched to controller
Collect second data point for calibration accuracy check,
tune controllers, observe control of HVAC system in each
mode of operation, and observe the operation of safety
11. EMCS INTERFACE WITH STANDARD LOCAL CONTROL PANELS. There are three feasible
methods of interfacing the standard SLDC control panel with an EMCS or UMCS. A demonstration
project at Fort Riley Kansas and associated research compared the analog/binary interface method to a
switches. In deciding whether or not and how to interface the control panel with EMCS, the designer
should consider the advantages and disadvantages associated with the available interface methods.
a. EMCS interface using analog and binary signals. The standard HVAC control panel designs
include terminal blocks designated for interfacing with an EMCS using 4-20 milliampere (analog)
input/output (I/O) signals and binary I/O signals. The analog I/O signals are used to interface the EMCS
with the controller process variable retransmission and control point adjustment. The binary (contact
closure) I/O signals are used to interface the EMCS with control panel shutdown and status devices and
to override the control panel.
(1) Analog outputs to EMCS. Process variable retransmission (PVR) is a 4-20 milliampere
analog output signal from each controller that is identical to the 4-20 milliampere PV input to the
controller. The control system design will show HVAC control panel terminal blocks showing connections
for interfacing controller process variable retransmission with EMCS.
(2) Analog inputs from EMCS. Control point adjustment (CPA) is a 4-20 milliampere analog
input signal available to the controller that provides for adjustment of controller setpoints. The control
system design will show HVAC control panel terminal blocks and wiring that allow connection of the CPA
signal, from an EMCS device, to the controller 4-20 milliampere remote-setpoint input terminals.
(3) Binary outputs to EMCS. Freezestats and smoke detectors operate relays, located inside the
control panel, as part of the HVAC control system shutdown circuits. Contacts of these relays are wired
to terminal blocks in the HVAC system control panel for EMCS use. The economizer controller operates
a relay located inside the control panel. A contact on this relay will be wired to terminal blocks in the
HVAC system control panel for EMCS use. Differential pressure switches across the air handling system
filters will have a contact in the device reserved for EMCS use.
(4) Binary inputs from EMCS. The control system ladder diagrams and HVAC control panel
details will show provisions for override of HVAC control panels by:
(a) Replacing HVAC control panel time clocks with EMCS start-stop contacts.
(b) Installing EMCS override of the HVAC system's economizer controller signal.
(5) The advantages of this method of interface are: