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National Instruments NI USB-7855R, User Manual

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National Instruments NI USB-7855R User Manual Download Page 6

Figure 4. Connecting Non-Referenced Single-Ended Signals to the NI USB-7855R

PGIA

ADC

AI+

NI USB-7855R

Connection

Accessory

AISENSE

AIGND

V

cm

V

1

+

–

+

–

Overvoltage

Protection

AI–

Overvoltage

Protection

Overvoltage

Protection

Connecting Differential Voltage Signals

You can connect grounded or floating differential signal sources to the NI USB-7855R.
Connect the positive voltage signal to the AI+ and the negative voltage signal to AI-. To
connect grounded differential signals to the NI USB-7855R, you must also connect the signal
reference to AI GND.

Figure 5. Connecting Grounded Differential Signals to the NI USB-7855R

PGIA

ADC

AI+

NI USB-7855R

Connection

Accessory

AISENSE

AIGND

V

cm

V

1

+

–

+

–

Overvoltage

Protection

AI–

Overvoltage

Protection

Overvoltage

Protection

To connect floating differential signals to the NI USB-7855R, you must connect the negative
and positive signals to AI GND through 1 MΩ resistors to keep the voltage within the
common-mode voltage range. If the voltage source is outside the common-mode voltage
range, the NI USB-7855R does not read data accurately.

NI USB-7855R User Manual | © National Instruments | 5

Summary of Contents for NI USB-7855R

Page 1: ...onal Instruments USB 7855 Manual Get Pricing Availability at ApexWaves com Call Today 1 800 915 6216 Email sales apexwaves com https www apexwaves com modular systems national instruments r series USB 7855 ...

Page 2: ...lity Guidelines This product was tested and complies with the regulatory requirements and limits for electromagnetic compatibility EMC as stated in the product specifications These requirements and limits are designed to provide reasonable protection against harmful interference when the product is operated in its intended operational electromagnetic environment This product is intended for use in...

Page 3: ...ide Hardware Overview The following high level block diagram represents the NI USB 7855R Figure 1 NI USB 7855R Block Diagram Device Temperature Overvoltage Protection Overvoltage Protection FPGA Temperature 40 MHz OSC AO x8 USB NI ASIC Kintex 7 FPGA NI USB 7855R Flash Memory DIO 5 V Reference DAC AO ADC AI CONNECTOR 0 DIO CONNECTOR 1 MIO Data Address Control AI x8 INA DIO x16 DIO x32 Overvoltage P...

Page 4: ... DIO9 DIO11 DIO13 DIO15 AO7 AO6 AO5 AO4 AO3 AO2 AO1 AO0 AISENSE AI7 AIGND6 AI6 AI5 AIGND4 AI4 AI3 AIGND2 AI2 AI1 AIGND0 AI0 5V DGND DGND DGND DGND DGND DGND DGND DGND DIO8 DIO10 DIO12 DIO14 AOGND7 AOGND6 AOGND5 AOGND4 AOGND3 AOGND2 AOGND1 AOGND0 NC AI7 AIGND7 AI6 AI5 AIGND5 AI4 AI3 AIGND3 AI2 AI1 AIGND1 AI0 68 34 67 33 66 32 65 31 64 30 63 29 62 28 61 27 60 26 59 25 58 24 57 23 56 22 55 21 54 20 5...

Page 5: ...ded or differential voltage signals Use the AISENSE pin to connect non referenced single ended signals Connecting Single Ended Voltage Signals To connect referenced single ended voltage signals to the NI USB 7855R you must connect the voltage ground signal to AI GND in order to keep the common mode voltage in the specified range as shown in Figure 3 Figure 3 Connecting Referenced Single Ended Sign...

Page 6: ...tial signals to the NI USB 7855R you must also connect the signal reference to AI GND Figure 5 Connecting Grounded Differential Signals to the NI USB 7855R PGIA ADC AI NI USB 7855R Connection Accessory AISENSE AIGND Vcm V1 Overvoltage Protection AI Overvoltage Protection Overvoltage Protection To connect floating differential signals to the NI USB 7855R you must connect the negative and positive s...

Page 7: ...nect a load Figure 7 Connecting a Load NI USB 7855R Connection Accessory AOGND LOAD AO DAC Digital I O The NI USB 7855R provides connections for 48 digital input output DIO channels Connector 0 contains 32 high speed DIO channels that can run up to 80 MHz signal frequencies and Connector 1 contains 16 low speed channels that can run up to 10 MHz signal frequencies Each connector has selectable log...

Page 8: ...t as input low with pull down resistors To set another power on state you can configure the NI USB 7855R to load a VI when the system powers on The VI can then set the DIO lines to any power on state All the high speed DIO channels on Connector 0 are routed with a 50 Ω characteristic trace impedance Route all external circuitry with a similar impedance to ensure best signal quality NI recommends p...

Page 9: ...distance To reduce the magnetic coupling between lines separate them by a reasonable distance if they run in parallel or run the lines at right angles to each other Do not run signal lines through conduits that also contain power lines Protect signal lines from magnetic fields caused by electric motors welding equipment breakers or transformers by running them through special metal conduits Mounti...

Page 10: ...ws Tighten the screws to a torque of 0 4 N m 3 6 lb in 2 Clip the bracket onto the DIN rail as shown Figure 10 DIN Rail Clip Parts Locator Diagram 1 2 3 1 DIN Rail Clip 2 DIN Rail Spring 3 DIN Rail 3 Place the NI USB 7855R on the backpanel wall mount with the signal wires facing down and the device bottom sitting on the backpanel wall mount lip 4 While holding the NI USB 7855R in place attach the ...

Page 11: ...criptions Symbol LED Description POWER Solid blue when the power is on USB READY Solid blue when the USB is ready ERROR Solid red for error cases 1 USER USER1 Blue user defined 2 USER USER2 Blue user defined 3 USER USER3 Blue user defined The following figure shows the LEDs on the front panel of the NI USB 7855R 10 NI USB 7855R User Manual ni com ...

Page 12: ...Instruments is not liable for damage resulting from such a connection The power rating is 4 75 to 5 1 VDC at 0 5 A Autonomous Mode You can run the NI USB 7855R without a USB connection to a host computer using Autonomous Mode To collect data the NI USB 7855R acquires in Autonomous Mode you must reconnect the NI USB 7855R to a host computer Caution Data is lost and is not recoverable upon reconnect...

Page 13: ...elp resources to email and phone assistance from NI Application Engineers National Instruments corporate headquarters is located at 11500 North Mopac Expressway Austin Texas 78759 3504 National Instruments also has offices located around the world to help address your support needs For telephone support in the United States create your service request at ni com support and follow the calling instr...

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