National Instruments NI 6520 User Manual

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National Instruments NI 6520 User Manual Manual pdf 13 page image

© National Instruments Corporation 13 NI 6520/6521 User GuideOptically Isolated Differential InputsThe input lines on the NI 6520/6521 device provide 8 lines of opticallyisolated digital input. These inputs contain an AC input photocoupler and aresistor for current limiting. The maximum input voltage (VIN) on theselines is 30 VDC.(NI 6520 Only) The input (VIN) range on the channels is –30 VDC to+30 VDC, for signals connected between P0.X+ to P0.X–, where X isline <0..7>.Sensing DC VoltagesThe NI 6520/6521 can sense DC signals from 11 V to DC power supplylevels up to 30 V.Input voltages between –4 V to +4 V produce a logic low. Input voltagesbetween –30 V to –11 V or between +11 V to +30 V produce a logic high.The logic state of signals between –11 V to –4 V and +4 V to +11 V is notdefined. This corresponds to standard industrial 24 V logic thresholds.There should never be more than a 30 V difference in P0.X+ and P0.X–terminals. Exceeding 30 V differential voltage could cause damage to thephotocouplers.(NI 6521 Only) The 30 V differential voltage can have up to ±120 Vcommon-mode voltage compared to chassis/digital ground of the NI 6521device.12, 30, 14, 32, 16, 34, 18,36P0.<7..0>+ Isolated input ports, positive terminals—Each ofthese terminals serves as the signal input. You canconnect either end of the input signal to it, regardlessof whether the level is positive or negative.13, 31, 15, 33, 17, 35, 19,37P0.<7..0>– Isolated input ports, negative terminals—Each ofthese terminals serves as the signal input. You canconnect either end of the input signal to it, regardlessof whether the level is positive or negative.Table 3. NI 6520/6521 Signal Descriptions (Continued)Pin Signal Name Description