199
JOHNSON CONTROLS
FORM 201.21-NM4 (616)
199
JOHNSON CONTROLS
8
Current Sensing and Scaling
Individual current transformers on each leg sense three
phases of output current on each compressor. These sig-
nals are buffered, divided by 2, and filtered by an RMS
to DC converter. The highest of the currents in the three
phases of each compressor leaving the RMS converters
is then sent to an A-D converter scaled, monitored by
the VSD Logic Board overload and high current protec-
tion circuitry, and sent to the Chiller Control Board for
display as the compressor current.
In order to set the motor overload level (determined by
the setting of the OVERLOAD ADJUST potentiometer
on the VSD Logic Board), the voltage level on the wip-
ers of the four OVERLOAD ADJUST potentiometers is
continuously sensed by the VSD Logic Board for current
protection and sent to the Chiller Control Board for both
display purposes and for current limiting control. This
parameter is the 105% FLA value.
VSD OPERATION AND CONTROLS (CON'T)
TABLE 12 - VSD OPERATING DISPLAY PARAMETERS
DATA
DISPLAY
FORMAT
Highest Phase of Compressor
Motor Current in Amperes RMS
(per Compressor)
XXX Amps
VSD Output Frequency
XXX.X Hz
Motor Overload Setting
(105% FLA potentiometer setting)
in amperes RMS
(per Compressor)
XXX Amps
DC Bus Voltage in DC Volts
(maximum of 2)
XXX Volts
VSD Internal Ambient Temperature
XXX.XºF
(or ºC)
IGBT Power Assembly Power Module
Highest Baseplate Temperature
(maximum of 2)
XXX.XºF
(or ºC)
Pre-Charge Enable Signal
(maximum of 2)
On or OFF
VSD cooling Fan/Pump
On or OFF
Compressor Run Status
(maximum of 4)
On or OFF
VSD Transmitted Operating parameters
VSD operating parameters will be transmitted to the
Chiller Control Board over the RS-485 communica-
tions link between the 2 boards. These values will be
displayed on the control panel display. The data and
display format are outlined in the TABLE 12 below:
