GE C30 Instruction Manual page 55

3 HARDWARE
is set to "On = 1" when the current flowing through the closed contact exceeds about 80 to 100 mA. The voltage monitor is
intended to check the health of the overall trip circuit, and the current monitor can be used to seal-in the output contact until
an external contact has interrupted current flow. If enabled, the current monitoring can be used as a seal-in signal to ensure
that the form-A contact does not attempt to break the energized inductive coil circuit and weld the output contacts.
Block diagrams are shown as follows for form-A and solid-state relay outputs with optional voltage monitor, optional current
monitor, and with no monitoring. The actual values shown for contact output 1 are the same for all contact outputs. Form-A
contact output with or without a current or voltage monitoring option is not polarity sensitive. The polarity shown in the figure
is required for solid-state contact output connection.
Figure 3–12: FORM-A AND SOLID-STATE CONTACT OUTPUTS WITH VOLTAGE AND CURRENT MONITORING
The operation of voltage and current monitors is reflected with the corresponding FlexLogic™ operands (
, and
CONT OP # VOFF CONT OP # ION
the voltage monitor is breaker trip circuit integrity monitoring; a typical application of the current monitor is seal-in of the
control command.
Refer to the Digital elements section of chapter 5 for an example of how form-A and solid-state relay contacts can be
applied for breaker trip circuit integrity monitoring.
Consider relay contacts unsafe to touch when the unit is energized.
USE OF FORM-A AND SOLID-STATE RELAY OUTPUTS IN HIGH IMPEDANCE CIRCUITS
For form-A and solid-state relay output contacts internally equipped with a voltage measuring circuit across the con-
NOTE
tact, the circuit has an impedance that can cause a problem when used in conjunction with external high input
impedance monitoring equipment such as modern relay test set trigger circuits. These monitoring circuits may con-
tinue to read the form-A contact as being closed after it has closed and subsequently opened, when measured as
an impedance.
The solution to this problem is to use the voltage measuring trigger input of the relay test set, and connect the form-
A contact through a voltage-dropping resistor to a DC voltage source. If the 48 V DC output of the power supply is
used as a source, a 500 Ω, 10 W resistor is appropriate. In this configuration, the voltage across either the form-A
contact or the resistor can be used to monitor the state of the output.
GE Multilin
) which can be used in protection, control, and alarm logic. The typical application of
C30 Controller System
3.2 WIRING
3
,
CONT OP # VON
3-11