Honeywell W7761A - Manual (Page 43)

EXCEL 10 W7761A INPUT/OUTPUT DEVICE
43 74-2699
The T7770A,B,C,D wall module is the room space temperature sensor—(current feature that can be used with the RIO
Device). When it is configured, it provides the temperature input that can be shared with the W7750 or W7751 controllers. If
there are multiple space sensors in a area controlled by one W7750 CVAHU, then the space temperatures can be wired into
the W7761A controller and mapped to the Zone Manager. The Zone Manager can average all of the space temperatures and
then have that value can be bound to the W7750 controlling that area.
Window Sensor (StatusWndw)
The digital input for a window contact can be wired into the W7761A device and then bound to a W7750 CVAHU to disable its
temperature control algorithm if someone has opened a window or door in the room or area that the W7750 is serving. When a
window is detected to be Open (digital input contacts Open equals window open), the normal temperature control is disabled,
and the W7750 Controller enters the Freeze Protect mode. Freeze Protect mode sets the space setpoint to 50 °F (10°C) and
brings on the fan and heat if the space temperature falls below this setpoint. Normal temperature control resumes on window
closure.
Dirty Filter Monitor
The air filter in the air handler can be monitored by a digital input in the W7761A and an alarm issued by the Zone Manager
when the filter media needs replacement. The two methods of monitoring the filter are:
1. A differential pressure switch whose contacts are connected to a digital input on the W7761A and;
2. A 2 to 10V differential pressure sensor wired to a voltage input on the W7761A. If the analog input sensor is used, its
measured value 0 to 5 inw (0 to 1.25 kPa) is compared to a user-selectable setpoint in the Zone Manager, the
comparison is done in the Zone Manager - valid range: 0 to 5 inw (0 to 1.25 kPa), and the Dirty Filter alarm is issued by
the Zone Manager when the pressure drop across the filter exceeds the setpoint.
Series 60 Modulating Control
Series 60 Control is also commonly referred to as Floating Control. The Excel 10 W7761A Device can drive Series 60 type
actuators to control a modulating damper or valve actuator. The W7761A device contains no control software, so these outputs
would have to be bound to either the Zone Manager or other Excel 10 controllers. When floating control is used, the full-stroke
motor drive time of the actuator must be entered into the configuration parameter DO1FlSpeed (for output 1), DO2FlSpeed (for
output 2). When Floating control is configured, two digital outputs are required, so the user has to change the configuration
parameter for the appropriate digital outputs.
Pulse Width Modulating (PWM) Control
The Excel 10 W7761A device can drive a PWM-type actuator to control a modulating actuator. The W7761A device contains
no control software, so these outputs would have to be bound to either the Zone Manager or other Excel 10 controllers. PWM
control positions the actuator based on the length, in seconds, of the pulse from the digital output. The controller outputs a
pulse whose length consists of two parts, a minimum and a maximum. The minimum pulse time represents the analog value of
zero percent (also indicates a signal presence) and the maximum pulse length that represents an analog value of 100 percent.
If the analog value is greater than zero percent, an additional time is added to the minimum pulse time. The length of time
added is directly proportional to the magnitude of the analog value. If PWM control is used, the configuration parameters for
the PWM operation must be specified. These parameters are DO1PWMPeriod and PWMZeroScale, and PWMFullScale.
Example: To find the pulse width of a valve actuator (for example stroke mid position - 50 percent) with the PWMZeroScale =
0.1 seconds, PWMFullScale = 25.5 seconds, and the PWMPeriod = 25.6 seconds. There are 256 increments available, so the
number of increments required for 50 percent would be (0.5 X 256) or 128. The time for each increment for this industry
standard pulse time is 0.1 seconds. The pulse width is the minimum time (0.1 second) + the number of increments (128 times
the seconds added 0.1) = 12.9 seconds. The W7750B Controller would command the valve output on for 12.9 seconds every
25.6 seconds to maintain the valve position at 50 percent.
Indoor Air Quality (IAQ) Override
The Excel 10 W7761A Device can monitor an IAQ sensor and that input can be bound to a W7750 CVAHU Controller that
supports an IAQ override feature, that upon detection of poor air quality in the space, allows the economizer dampers to be
opened above the standard minimum position setting to a value set in EconIAQPos (parameter located in W7750). Two
different methods of detecting poor air quality are supported, The first is by using an IAQ switch device connected to a digital
input on the W7761A Device, where a contact closure indicates poor air quality. This digital input would then be bound to the
W7750 Controller that is serving the area being monitored and would initiate the IAQ override mode. The second is through an
analog input that connects to a CO
2
Sensor (0 to 10V). The measured value of CO
2
from this sensor (0 to 2000 ppm) is
mapped into the Zone Manager where it is compared to a setpoint (parameter located in the Zone Manager). When the CO
2
level is higher than the setpoint, the Zone Manager can initiate an IAQ alarm. A pseudo digital point in the Zone Manager can
be bound to the W7750 CVAHU Controller which can initiate the IAQ override mode.