Daikin RoofPak RPS Series Installation And Maintenance Manual page 117

Pressure Sensors
The MicroTech III controller uses 0 to 5" W.C. static pressure
transducers for measuring duct static pressure. As the duct
static pressure varies from 0-5" W.C., the transducer output
will vary from 4-20mA. The transducer output signal is 420mA
however the signal entering the VFD is converted to a DC
signal via a 500 Ohm resistor across the output signal at the
transducer.
If building static pressure control is provided, a -0.25" W.C. to
0.25" W.C. static pressure transducer is used. As the building
static pressure varies from -0.25" W.C. to 0.25" W.C., the
transducer output will vary from 4-20mA. The transducer
output signal is 4-20mA however the signal entering the VFD
is converted to a DC signal via a 500 Ohm resistor across the
output signal at the transducer.
Troubleshooting Pressure Transducers
Use the following procedure to troubleshoot a suspect sensor:
If the duct static pressure always reads 0" WC on the unit
keypad/display and the VFD speed is continuously ramping to
100%, check the following:
If the unit has two duct static pressure sensors (SPS1 and
SPS2), verify that they both function properly per the following
procedure. Also check for faulty wiring connections at the VFD
analog inputs.
The controller displays and controls to the lower of the two
readings. If a sensor is defective and inputs 0 volts to the VFD,
the static pressure reading on the keypad/display reads 0 and
the controller attempts to increase the 0 value to set point by
ramping the VFD up.
If a second sensor (SPS2) is not installed or the pressure
tubing to it is not connected, make sure the 2nd DSP Sensor=
parameter in the Unit Configuration menu of the keypad/
display is set to "No" so that the controller ignores the second
static pressure analog input.
www.DaikinApplied.com
If a second sensor (SPS2) is installed, make sure the 2nd
DSP Sensor= parameter in the Unit Configuration menu of the
keypad/display is set to "Yes."
Check the 24 VDC power supply to the sensor, verify that there
is 24 VDC between the suspect transducer "+" and "-" terminals.
Using an accurate manometer or gauge, measure the same
pressure that the suspect transducer is sensing. To do this, tap
into the transducer high and low pressure tubing or locate the
measurement device taps next to the transducer taps.
If the suspect sensor is measuring duct static pressure, verify
that the high and low pressure taps are properly installed.
An improper pressure tap installation can cause severe
fluctuations in the sensed pressure. Refer to the model-specific
installation manual for pressure tap installation guidelines.
Measure the DC voltage output from the transducer across the
sensor "S" and "-" terminals.
If the measured voltage and pressure do not match, there
may be a wiring problem, the factory 500 ohm resistor across
"S" and "-" or the transducer may be defective. Check the
transducer input circuit wiring and connections for defects.
If the measured voltage and pressure match, the VFD
parameters and/or ModBus communication between the
controller and the VFD will need to be verified.
Remove powers from the controller by opening system switch
S1. If available, swap a similar good transducer with the
suspect transducer or try installing a new transducer. Restore
power by closing S1 and verify whether the suspect transducer
is defective.
117 IM 926-3 • ROOFPAK APPLIED SYSTEMS
Maintenance and Service