Figure 3–13: 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 # VOFF
the voltage monitor is breaker trip circuit integrity monitoring; a typical application of the current monitor is seal-in of the
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-
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
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.
Wherever a tilde "~" symbol appears, substitute with the slot position of the module; wherever a number sign "#"
appears, substitute the contact number
When current monitoring is used to seal-in the form-A and solid-state relay contact outputs, the Flex-
Logic™ operand driving the contact output should be given a reset delay of 10 ms to prevent damage
of the output contact (in situations when the element initiating the contact output is bouncing, at val-
ues in the region of the pickup value).
) 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.
L60 Line Phase Comparison System
CONT OP # VON