GE C30 Instruction Manual page 60

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 the current is above about 1 to 2.5 mA, and the current monitor is set to "On = 1" when the current 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.
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.
3
Figure 3–14: 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
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.
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 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 , 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.
3-12
) which can be used in protection, control, and alarm logic. The typical application of
CONT OP # ION
Consider relay contacts unsafe to touch when the unit is energized. If the relay contacts need
to be used for low voltage accessible applications, ensure proper insulation levels.
C30 Controller System
3 HARDWARE
,
CONT OP # VON
GE Multilin