WattMaster WCC III part 12 - Manual (Page 46)

WCC III Technical Guide 12-44
12. WCC III INSTALLATION
0 - 1, 0 – 5, 0 - 10 VDC, and Thermistor
Type Sensors
The SAT III controller can accept a 0-1VDC, 0-5VDC, 0-10VDC,
or THERM signal from a sensor. Since the SAT III controller is
designed with eight settable analog input jumpers, these eight
analog input jumpers must be correctly set for the type of input that
is needed for the desired VDC across the load resistor to represent
the full scale value of the analog input. On the older SAT II
controller, the voltage from the 0-10 and 0-5 VDC sensors needed
to be reduced before it reached the analog inputs of the older SAT
II controller. This was accomplished by placing a line resistor in
the circuit in addition to the load resistor.
“Older” 2-Wire Flush Mount Sensors
Wiring connections for the “older” 2-Wire Flush mount sensors
is as follows: The “+V” terminal on the SAT III controller is a
+12 VDC power source, and the ATI connection from the “older”
2-Wire Flush mount sensor is then connected to the SAT III ATI
input(s). The temperature sensor is a current transducer which
transmits a current proportional to the temperature it is sensing.
The load resistor on the front of the SAT III controller is in series
with the temperature sensor and connects the “ATI” terminal to
the “GND” terminal. The satellite controller then monitors the
voltage between the “ATI” terminal and “GND” on the SAT III
controller to determine the temperature that is then sensed by the
sensing element of the 2-wire Flush mount sensor. The SAT III
controller could use either a 1-VDC or a 5-VDC input for the
“older” 2-wire Flush mount sensor. With a 1-VDC input between
“ATI” and “GND” to represent the 100 percent scale value on the
Analog Input Screen, and 0 VDC represents the 0 percent scale
value. The maximum allowable voltage across the load resistor is
1.2 volts. This is with the 0-1V analog input jumper installed. With
the 0-5V analog input jumper installed, the satellite controller is
designed for 5 VDC between “ATI” and “GND” to represent the
500 percent scale value on the Analog Input Screen, and 0 VDC
represents the 0 percent scale value. The maximum allowable
voltage across the load resistor is 5.2 volts with the 0-5V analog
input jumper installed.
The specifi cations of the temperature sensor determine the value
of the SAT III load resistor and the 0 percent and 100 percent scale
value on the Analog Input Screen. The load resistors must be fi eld
installed.
The older 2-wire air/water temperature sensor was used to monitor
the temperature of the air in duct work or the temperature of fl uid
in a pipe. For fl uid pipe applications, the probe may be removed
from the transmitter, strapped to the pipe, and thermally insulated
from the ambient air. The transmitter should be mounted remotely
by extending the two wires connecting the probe to the transmitter.
The transmitter may be located up to 100 feet from the probe, or
the sensor may be mounted in an immersion well with the use of
thermal compound to ensure good thermal conduction between
the water and the sensor. For chilled water sensing, it is highly
recommended that the sensing element be removed from the
transmitter (control head) to prevent condensation in the head.
The air/water sensor has two temperature ranges available,
depending on which load resistor is used. A 100 ohm load resistor
gives the sensor a control range of 30-120°F, and a 49.9 ohm load
resistor gives the sensor a control range of 40-240 °F. This is with
either the 0-1V or 0-5V analog input jumper installed. 100 percent
scaling must be changed between the “Units @ 0% scale” and the
“Units @ full scale” on the Analog Input Screen.
NOTE: These 2-wire based sensors are now considered
obsolete. When any 2-wire based sensor fails, a replacement
thermistor type sensor is available for replacement for the SAT
III controller.
“Older” 3-Wire Voltage Type
Temperature Sensors
The older 3-wire temperature sensors accomplish the same thing
as the older 2-wire sensors, only you can think of the load resistor
as being in the sensor and not at the satellite controller. The 3-wire
sensor is wired to the “+V,” “ATI,” and “GND” terminals on the
SAT III controller. The 3-wire sensor transmits a voltage between
“ATI” and “GND” that directly corresponds to temperature, and
therefore, a load resistor at the SAT III controller is not required
when using a 3-wire voltage type sensor. 3 – wire sensors should
not be used for long distance wiring, as wire length will affect
the voltage coming back from the sensor. This voltage is again
proportional to the temperature, so a 0.1 volt voltage drop is
actually equivalent to a 10 deg °F error in temperature. 200 feet
is about the maximum distance for a 3-wire sensor due to voltage
drop of the small gauge wire (18 gauge and lower) that sensors are
typically wired with.
NOTE: These 3-wire based sensors are now considered
obsolete, and when any 3-wire based sensor fails, a
replacement thermistor type sensor is available for the SAT III
controller.
Temperature Sensors