GE C30 Instruction Manual page 61

3 HARDWARE 3.2 WIRING
Some form-A / solid-state relay outputs include circuits to monitor the DC voltage across the output contact when it is open,
and the DC current through the output contact when it is closed. Each of the monitors contains a level detector whose out-
put is set to logic "On = 1" when the current in the circuit is above the threshold setting. The voltage monitor is set to "On =
1" when there is a voltage across open contact (the detector allows a current of about 1 to 2.5 mA), and the current monitor
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.
3
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 ( ,
CONT OP # VON
, and ) which can be used in protection, control, and alarm logic. The typical application of
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.
GE Multilin C30 Controller System 3-11