5-108 B90 Low Impedance Bus Differential System GE Multilin5.6 CONTROL ELEMENTS 5 SETTINGS5Figure 5–52: DIGITAL ELEMENT SCHEME LOGICCIRCUIT MONITORING APPLICATIONS:Some versions of the digital input modules include an active voltage monitor circuit connected across form-A contacts. Thevoltage monitor circuit limits the trickle current through the output circuit (see technical specifications for form-A).As long as the current through the voltage monitor is above a threshold (see technical specifications for form-A), the “ContOp 1 VOn” FlexLogic™ operand will be set (for contact input 1 – corresponding operands exist for each contact output). Ifthe output circuit has a high resistance or the DC current is interrupted, the trickle current will drop below the threshold andthe “Cont Op 1 VOff” FlexLogic™ operand will be set. Consequently, the state of these operands can be used as indicatorsof the integrity of the circuits in which form-A contacts are inserted.EXAMPLE 1: BREAKER TRIP CIRCUIT INTEGRITY MONITORINGIn many applications it is desired to monitor the breaker trip circuit integrity so problems can be detected before a trip oper-ation is required. The circuit is considered to be healthy when the voltage monitor connected across the trip output contactdetects a low level of current, well below the operating current of the breaker trip coil. If the circuit presents a high resis-tance, the trickle current will fall below the monitor threshold and an alarm would be declared.In most breaker control circuits, the trip coil is connected in series with a breaker auxiliary contact which is open when thebreaker is open (see diagram below). To prevent unwanted alarms in this situation, the trip circuit monitoring logic mustinclude the breaker position.Figure 5–53: TRIP CIRCUIT EXAMPLE 1SETTINGDIGITAL ELEMENT 01FUNCTION:Disabled = 0Enabled = 1DIGITAL ELEMENT 01BLOCK:Off = 0FLEXLOGIC OPERANDSDIG ELEM 01 DPODIG ELEM 01 PKPSETTING827042A1.VSDDIGITAL ELEMENT 01INPUT:Off = 0SETTINGINPUT = 1RUN tPKPtRSTDIGITAL ELEMENT 01PICKUP DELAY:SETTINGSDIGITAL ELEMENT 01RESET DELAY:ANDSETTINGDIGITAL ELEMENT 01NAME:DIG ELEM 01 OP7ULSFRLOD85VHULHVGHYLFHZLWKIRUP$FRQWDFWV, FXUUHQWPRQLWRU9 YROWDJHPRQLWRU'&²$&'5+D+E+F,9 '&
