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Calibration of Flow Sensor and Position
of Valves (Air and Water)
Calibration that is initiated via a reset is
staggered to prevent duct over pressur-
ization. The calibration process consists
of 2 steps:
1.Establishing the true valve position.
This is done by overdriving the valve
closed (open in the case when UCM4 is
configured for VariTrac Bypass Damper
Mode of operation) for 30 seconds
beyond the configured stroke time (water
valve stroke time plus 15 seconds).
2.Adjusting the D/A output to correct any
transducer offset.
The D/A output is fed into an op amp
along with the signal from the transducer
to remove any zero offset voltage from
the pressure transducer.
Communication Protocol Selection
UCM 4.0 can communicate using either
COM 3 or COM 4 protocols. The UCM will
automatically determine whether the
front-end system is a COM 3 or COM 4
device.
Adjustable Air Valve Stroke Times
Stroke times are adjustable for all units
over the communication link as long as
the communication protocol used is
COM 4. If the UCM is in COM 3 mode, the
stroke time is only configurable for
generic and VariTrane Series F configura-
tions. Stroke times for non-generic, non-
series F COM 3 systems are hard coded
into the UCM for the following valves:
Series F All sizes
Series D & E Sizes 3, 6, and 11
Series D & E Sizes 17 , 24, 32, and 42 6 minutes
VariTrac Round
VariTrac Rectangular
Series C Sizes all but 20, 40
Series C Sizes 20, 40
Timed Override (TOV) Button Functions
There are two buttons that the user can
access. Pushing the timed override
button (on) in an unoccupied period
provides two hours of occupied control.
The UCM will switch into occupied mode
and control to the occupied set points for
two hours. The cancel button stops a
timed override sequence and returns to
unoccupied control. The UCM will revert
back to unoccupied mode immediately.
16
UCM Programming
and Operation
Timed override (TOV) and cancel
buttons are recognized if they have
been pushed for at least 0.5 seconds
and no more than 15 seconds. Pushing
the buttons for longer than 15 seconds
will simulate a zone temperature sensor
failure. The failure is non-latching and
ceases as soon as the button is
released.
"*" And "**" Functions
Also in conjunction with the
thumbwheel, the timed override button
can cause an override to maximum
flow or unoccupied. The TOV button
must be pushed for at least 2 seconds
and no more than 15 seconds with the
thumbwheel in one of the override
positions to recognize an override
condition. With the thumbwheel in the
"*" position an override to maximum
flow is generated. With the thumbwheel
in the "**" position an override to
unoccupied is generated. The maxi-
mum flow and unoccupied overrides
are held until the thumbwheel is moved
into the normal operating region.
Note: If the thumbwheel is not enabled,
locally generated overrides ("*" or "**")
are not possible.
Local Occupancy detector.
Local occupancy detection was added
with UCM4 on input TB4-1. TB4-1 is a 24
VAC input operated in a negative logic
mode wherein the absence of signal
indicates occupancy and the presence
90 seconds
of 24 VAC indicates non-occupancy. The
6 min. 24 sec.
occupancy detector's interface is two
57 seconds
dry relay contacts. Relay closure (short
60 seconds
between two dry relay contacts and
7 min. 12 sec.
presence of 24 VAC at TB4-1) shall
9.25 min.
indicate unoccupancy. The VAV UCM
has a COM 4 configuration bit to
indicate if the VAV UCM has an occu-
pancy sensor connected.
When configured for an occupancy
sensor and communications are active,
an occupancy input state will be
reflected by the UCM to an upper level
system controller. The upper level
system controller is responsible for
causing any system changes necessary
to provide occupied control.
When configured for an occupancy
sensor and communications are not
active and occupancy is detected, the
UCM shall transition to the occupied
mode of operation. Upon loss of the
occupancy indication from the
occupancy detector, the VAV UCM will
revert back to unoccupied mode.
When configured for an occupancy
sensor and communications are active,
loss of COM 4 communications does
not result in the VAV UCM defaulting to
occupied mode.
When configured as a generic input
and communications are active an
occupancy input state will be reflected
by the UCM to an upper level system
controller. The upper level system
controller shall be responsible for
causing any system changes necessary
to provide occupied control. When
configured for generic mode, loss of
COM 4 communications will result in
the UCM defaulting back into occupied
mode.
Reheat Control
Reheat operation is allowed provided
the following conditions are satisfied:
1. The unit is not calibrating.
2.Flow overrides (open or closed) are not
in affect.
3.Reheat lockout is not enabled.
4.If maximum flow override or fan
lockout is present then parallel fan with
any electric heat is not allowed.
5.If the zone temperature sensor has
failed cold (open), reheat is not allowed.
6.While in the heat mode only hot water
heat can be used. If using auto
changeover, UCM 3.3 and later will
enable electric heat in the heat mode if
the auxiliary temperature is less than
the electric heat on set point and will
disable electric heat when the auxiliary
air temperature is greater than the
electric heat off set point.
Modulating Hot Water Reheat
When the zone temperature reaches the
heating set point + 0.5°F the reheat is
turned completely off. The modulating
hot water valve is over driven closed
(by 15 seconds) any time reheat is no
longer required.
VAV-SVX01B-EN
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