GE 489 - Manual (Page 28)

2-12 489 Generator Management Relay GE Multilin
2.2 ELECTRICAL 2 INSTALLATION
2
2.2.8 ANALOG OUTPUTS
The 489 provides four analog output channels, which when ordering, are selected to provide a full-scale range of either
0 to 1 mA (into a maximum 10 k
Ω impedance), or 4 to 20 mA (into a maximum 600 Ω impedance). Each channel can be
configured to provide full-scale output sensitivity for any range of any measured parameter.
As shown in Figure 2–9: Typical Wiring Diagram on page 2–7, these outputs share one common return. The polarity of
these outputs must be observed for proper operation. Shielded cable should be used, with only one end of the shield
grounded, to minimize noise effects.
The analog output circuitry is isolated as a group with the Analog Input circuitry and the RTD circuitry. Only one ground ref-
erence should be used for the three circuits. Transorbs limit this isolation to ±36 V with respect to the 489 safety ground.
If a voltage output is required, a burden resistor must be connected at the input of the SCADA measuring device. Ignoring
the input impedance of the input:
(EQ 2.1)
For example, for a 0 to 1 mA input, if 5 V full scale corresponds to 1 mA, then R
LOAD
= 5 V / 0.001 A = 5000 Ω. For a
4 to 20 mA input, this resistor would be R
LOAD
= 5 V / 0.020 A = 250 Ω.
2.2.9 RTD SENSOR CONNECTIONS
The 489 can monitor up to 12 RTD inputs for Stator, Bearing, Ambient, or Other temperature monitoring. The type of each
RTD is field programmable as: 100
Ω Platinum (DIN 43760), 100 Ω Nickel, 120 Ω Nickel, or 10 Ω Copper. RTDs must be
three wire type. Every two RTDs shares a common return.
The 489 RTD circuitry compensates for lead resistance, provided that each of the three leads is the same length. Lead
resistance should not exceed 25
Ω per lead. Shielded cable should be used to prevent noise pickup in the industrial envi-
ronment. RTD cables should be kept close to grounded metal casings and avoid areas of high electromagnetic or radio
interference. RTD leads should not be run adjacent to or in the same conduit as high current carrying wires.
Figure 2–15: RTD WIRING
IMPORTANT NOTE: The RTD circuitry is isolated as a group with the Analog Input circuitry and the Analog Output
circuitry. Only one ground reference should be used for the three circuits. Transorbs limit this isolation to ±36 V with
respect to the 489 safety ground. If code requires that the RTDs be grounded locally at the generator terminal box,
that will also be the ground reference for the analog inputs and outputs.
R
LOAD
V
FULL-SCALE
I
MAX
---------------------------------- =
3 WIRE SHIELDED CABLE
RTD
TERMINALS
RTD TERMINALS
AT GENERATOR
Maximum total lead resistance
25 ohms (Platinum & Nickel RTDs)
3 ohms (Copper RTDs)
OPTIONAL GROUND
Shield is internally
connected to safety
ground terminal G12
Route cable in separate conduit from
current carrying conductors
RTD IN
GENERATOR
STATOR
OR
BEARING
808761E4.CDR
B1
A1
A2
A3
HOT
COMPENSATION
RETURN
SHIELD
CHASSIS
GROUND
RT
D
S
EN
S
IN
G
RT
D
#
1
489
RELAY
NOTE