BACNET® FIXED FUNCTION THERMOSTAT
31-00093—01
4
Grounding the MS/TP LAN Shield
Proper shield grounding of the MS/TP cabling can help
minimize the risk of communications problems and
damage to equipment because of transient voltage spikes
(for example, lightning strikes).
Follow these guidelines for grounding MS/TP cable
shields:
• Each MS/TP segment should have a single point of
shield ground, preferably as close to the middle of the
cabling run as possible.
• Do not ground the MS/TP shield using a BACnet FF
terminal.
• Never ground both ends of a shield; differences in
potential between the grounds may induce current on
the shield, causing interference.
• At termination connecting points, tie the shield through
with a wire nut.
• At ungrounded, exposed shield points (the end of a
segment), tape back the shield to the wire jacket or, for
optimum transient shunting, use 100V gas discharge
tubes or 120V MOVs between shield and ground.
Terminating Resistors
Matched terminating resistors wired across MS/TP+ and
MS/TP– are required at the last device on each end of the
MS/TP segment for signal integrity (Fig. 5).
Optimum segment performance typically requires
“tuning,” a process by which the value of the terminating
resistors is selected based on the wave form of signals on
the segment. View wave forms using an industrial scope
meter. The goal is to have as square a wave form as
possible with an amplitude greater than 200 mV. Resistors
affect the wave form as follows:
• When the resistance value decreases, the amplitude of
the wave form decreases and becomes more square.
• When the resistance value increases, the amplitude of
the wave form increases and becomes less square.
Typically, precision resistors in the range 80-130 Ohms
(+1%) yield acceptable results. Ideally, the value of the
terminating resistors should match the rated
characteristic impedance of the installed cable. For
example, if the installed MS/TP cable has a listed
characteristic impedance of 100 Ohm, install 100 Ohm
matched precision resistors.
CAUTION
Do not mismatch terminating resistors.
Ensure that both resistors on a segment have the
same value.
NOTE:
Typically, White is Data - and Black is Data +.
Fig. 5. Terminating resistor detail.
Mounting Thermostat to Wallplate
1.
Align the terminal screw blocks with the pins on the
back of the thermostat.
2.
Push the thermostat straight onto the wallplate.
Fig. 6. Thermostat mounting.
NOTE:
To remove the thermostat from the wall, first pull
out at the bottom of the thermostat; then remove
the top.
CONFIGURATION
Once the BACnet FF is mounted and wired, configure it
from the BACnet FF touchscreen.
Adjusting the Date and Time
When the controller is first powered up, the date and time
might need to be set. These are set at the factory, but the
on-board power supply may have run down. If this
happens, adjust the date and time.
TO ADJUST THE TIME
1.
Touch Clock at the bottom of the screen.
2.
Use the arrows to adjust the year, month, and day.
3.
Press DONE.
4.
Adjust the time and press DONE.
Setting the MAC Address and
Device Instance
The factory default MAC address is 0. Valid MAC
addresses are 0-127. The default device instance is
0009999. Valid device instances are 0-4194302.
NOTE:
The device instance can also be set using a
BACnet Supervisor
WALL
M19919
REMOVE DURING INST
ALLA
TION