WattMaster WM-WCC3-TGD-01B - Manual (Page 64)

1. GENERAL INSTRUCTIONS
WCC III Technical Guide 1-10
EA Driver
The EA Driver Mode is “3-point fl oating” control. For example,
assume that the H/C control outputs on channel 2 of the satellite
controller are used to control a VAV box using the EA Driver
Mode. When the space needs heat, the “COM” to “H” contacts on
the satellite controller will close to drive the damper in the VAV
box to the closed position. When the space needs cooling, the
“COM” to “C” contact on the satellite controller will close to open
the damper in the VAV box.
There are two Data Registers associated with an EA Driver Screen.
The value of the fi rst Data Register is equal to the setpoint entered
on the EA Driver Screen and is referred to as “RnA.” The value
of the second Data Register is equal to the difference between the
setpoint and the actual temperature and is referred to as “RnB.”
“R” stands for data register, and “n” refers to channel 1-8 of the
satellite controller.
RnA = Setpoint
RnB = Difference between Setpoint and Measured Value (error)
For example, assume that the setpoint for the room in question
is 72 °F, and the actual temperature is 70 °F. The value of Data
Register R2A (setpoint) is 72 °F, and the value of Data Register
R2B (error) is -2 °F, since the actual space temperature is 2 °F
below the setpoint.
The Data Register could be used to turn on a second stage of heat
whenever the space temperature falls 2 °F below setpoint. Assume
that the second stage of heat is a heating coil which is energized
when satellite controller contact K3h is closed. A Dual Limit Screen
is used to control contact K3h. Data Register R2B is entered as
the analog input value for the Dual Limit Screen. When the value
of R2B is -2 or less (the space temperature is at least 2 °F below
setpoint), contact K3h closes to turn on the second stage of heat.
Dual Limit
When the H/C control output contact on the satellite controller
is controlled by a Dual Limit Screen, the contact opens and
closes based on how the analog input value compares to a pair
of setpoints. There is one Data Register for each contact on the
satellite controller which is controlled by a Dual Limit Screen. The
value of the Data Register is the difference between the setpoint
and the actual temperature.
The Data Register for a Dual Limit Screen is named “RnA” or
RnB.” “R” stands for data register, “n” refers to channel 1-8 of the
satellite controller, “A” means the “COM” to “H” contact, and “B”
means the “COM” to “C” contact. Therefore, the Data Register for
contact Klh is R1A.
RnA = Difference between Setpoint and Measured Value
(COM to H)
RnB = Difference between Setpoint and Measured Value
(COM to C)
The Dual Limit Screen has two setpoints, the high limit and the low
limit. Since the Data Register is the difference between the setpoint
and the actual temperature, you have to “tell” the system what you
are considering the setpoint to be. Therefore, the Data Register is
measured from either the “Midpoint” or “Nearest Limit” of the
setpoints, depending on how the Dual Limit Screen is set up.
For example, assume that a Dual Limit Screen is used to control a
heat pump compressor to have the compressor off if the space is
between 70 and 74 °F. If the space temperature is below 70 °F, the
compressor will be on for heating, and if the space temperature is
above 74 °F, the compressor will be on for cooling. Assume the
actual space temperature is 76 °F.
The Data Register can be measured from either the “Midpoint”
or the “Nearest Limit.” If the Data Register is measured from the
“Midpoint,” the value of the Data is 4 °F.
Low Limit High Limit Actual Temperature
70 72 74 76
4 Deg
Midpoint
Data Register
Difference between actual temperature and the “Midpoint” of the
setpoints = 4 °F, and therefore, the value of the Data Register is 4
°F.
If the Data Register is measured from the nearest limit, the value of
the Data Register is 2 °F.
Low Limit High Limit Actual Temperature
70
74 76
2 Deg
Nearest
Limit
Data Register
Data Registers