Heavy Duty Balanced Opposed Compressors - Ariel Corporation

For Models: JGH:E:K:T Section 2 - Instrumentation
Resistance Temperature Devices (RTD’s)
An RTD is a resistor sensor in which electrical resistance accurately varies with temperature.
Appropriate electronic devices can interpret the resistance as temperature. Main bearing RTD’s are
dual-element RTD instrument assemblies, consisting of two RTD’s in each instrument for each main
bearing. Each element is a three-wire, 100 ohms (at 0°C), Alpha = 0.00385 ohms/ohm/°C, platinum
thin film sensor.
Wire: Use standard 24 AWG (American Wire Gage) instrumentation wire
from the junction box on the side of the compressor frame to sensor
wiring. Wire an RTD three-wire set using a 2, 3 or 4 wire lead system.
More wires increases system accuracy. Ariel recommends standard foil
shielded instrumentation cable runs from the compressor frame to control
panel. Ground shields in the control panel.
Sensor Accuracy: 100 + 0.12 ohms at 0°C = 1.1°F (0.6°C) or 0.6%.
Terminals: Use any standard terminals.
For each instrument, one RTD three-wire set connects to the monitoring
circuit. Insulate unused wire ends from each other and conduit ground.
Dual element RTDs allow for rewiring instead of replacing the instrument
if an element fails.
RTD's with two red wires and one white wire for one element, and two
black wires and one green wire for the other simplify wiring requirements.
Dual-element RTD redundancy allows operators to restore bearing
temperature monitoring without entering the crankcase for each RTD failure.
Alarm and Shutdown Limits
Element 1
Element 2
3/11 PAGE 2-13
White
Red
Red
Green
Black
Black
Figure 2-13 Dual Element
RTD Wiring Dia-
1. Main bearing temperature high alarm and shutdown. - Ariel recommends 20°F (12°C) above
normal operating temperature for alarm and 30°F (18°C) above for shutdown. Maximum values
of 220°F (104°C) for alarm and 230°F (110°C) for shutdown apply. Normal operating temperature
is the average of all main bearing temperatures at design load when oil temperature stabilizes
and all components are heat-soaked.
2. High main bearing temperature differential alarm and shutdown. - Main bearing differential
temperature is the difference between the maximum and minimum of all main bearing temperatures.
Ariel recommends 20°F (12°C) for alarm and 30°F (18°C) for shutdown. Be aware that
after a warm shutdown, main bearing #1 may cool faster than the others and prevent a restart.