Part 2

Plug-In Assembly Configuration 525For this reason, when making voltage measurements, NEVER input voltagesimultaneously into the rear panel terminals and the backplane connectors. This canhappen since the 3497A will support multiple channel closures in the Latch Mode.GCOM is the reference for the + 19V and -1 9V Analog Power Supplies. It can alsoserve as a common mode current if it is properly connected. Common mode voltagesare those signals which appear on both the HlGH and LOW voltmeter terminalssimultaneously and can cause reading errors if not properly handled. These voltagesare shown as Vcm in Figure 164.GUARDED MEASUREMENTS GUIDELINES0 Always know the potential of GCOM with respect to Earth ground.0 Always connect GCOM so that no common mode current flowsthrough any resistance which determines the input voltage he., theHlGH and LOW DVM input leads).0 Never exceed 170 V peak input between any two input terminals.Interconnecting Circuitry Using Both Supply ReferencesIf your application requires that you use one or more of the lnguard ReferencedPower Supplies (+ 5V Relay, + 5V Logic, + 15V L or -8V TC) with either of theGuard Referenced Power Supplies (+ 19V or -1 9V), the two references must beisolated from each other. The degree of isolation is 170 V minimum. A good wayto do this is to use optoisolators as shown in Figure 165. The inputs to the optoisolatorsshould be referenced to the lnguard section and the outputs referencedto GUARD COMMON.Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com