3.21 Main Menu - Compressor Functions -
Group 28
3.21.1 28-2* Discharge Temperature
Monitor
The Discharge Temperature Monitor (DTM) can be used to
prevent
the discharge temperature from reaching
dangerous levels.
Two temperature levels of increasing severity can be
programmed. These levels are called warning level (set in
28-24 Warning Level) and emergency level (set in
28-24 Warning Level) in order of increasing severity. Each
level corresponds to a icular set of preventive actions.
Illustration 3.70
Discharge temperatures above the Emergency level cause
an
alarm and an immediate trip to prevent damage to the
compressor.
Normal operations apply for discharge temperatures below
Warning level. The discharge temperature is passively
monitored without affecting frequency converter
operations.
Discharge temperatures in the range from Warning level to
Emergency level trigger a warning and an action set by
28-25 Warning Action. The action can be None or Decrease
cooling. If the action is set to Decrease cooling the cooling
is decreased as a preventive action in an attempt to lower
the discharge temperature.
Cooling is decreased by step-wise lowering of the shaft
speed until the discharge temperature either drops below
Warning level or exceeds Emergency level. Each step
represents a three minute period during which the
maximum allowed shaft speed is 10 Hz lower than the
previous
step. The initial step occurs when the discharge
temperature rises from below to above Warning level and
uses the current shaft speed as basis for the 10 Hz speed
reduction.
The speed steps enforce maximum shaft speeds. If the
reference corresponds to a lesser speed, the reference is
obeyed. If it corresponds to a higher speed, the speed is
limited to the maximum shaft speed for that step.
Illustration 3.71
NOTE
If the Cascade Controller is active unwanted staging or
destaging may result if the Discharge Temperature Monitor
reduces the speed to Motor Speed Low Limit, 4-11 Motor
Speed Low Limit [RPM] or 4-12 Motor Speed Low Limit [Hz].
28-20 Temperature Source
Option: Function:
Selects the input terminal to which the
discharge
temperature measurement device is
connected.
[0] * None No Source. The Discharge Temperature Monitor
is
not active.
[1] Analog
input
53
The measurement device is connected to input
terminal 53. Program 6-10 Terminal 53 Low
Voltage to 6-15 Terminal 53 High Ref./Feedb.
Value to match the characteristics of the
device.
[2] Analog
input
54
The measurement device is connected to input
terminal 54. Program 6-20 Terminal 54 Low
Voltage to 6-25 Terminal 54 High Ref./Feedb.
Value to match the characteristics of the
device.
28-21 Temperature Unit
Option: Function:
Selects the unit of the discharge temperature.
[60 ] * ˚C
[160] ˚F
Parameter Description
VLT
®
Refrigeration Drive Programming Guide
164 MG16H102 - VLT
®
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