GE B90 Instruction Manual page 56

WIRING
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 3-15: Form-A and solid-state contact outputs with voltage and current monitoring
3
The operation of voltage and current monitors is reflected with the corresponding FlexLogic operands
VOFF, and
OP # CONT OP #
monitor is breaker trip circuit integrity monitoring; a typical application of the current monitor is seal-in of the control
command.
See 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
contact, 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 can
continue 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 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.
3-16
ION) that can be used in protection, control, and alarm logic. The typical application of the voltage
Consider relay contacts unsafe to touch when the unit is energized. Death or serious injury can
result from touching live relay contacts.
B90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHAPTER 3: INSTALLATION
(CONT OP #
VON, CONT