Omega Speaker Systems PCI-DAS1001, PCI-DAS1002 manual Differential Inputs

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Differential Inputs

Differential inputs measure the voltage between two distinct input signals. Within a certain range (referred to as the common mode range), the measurement is almost independent of signal source to PCI-DAS1000 ground variations. A differential input is also much more immune to EMI than a single-ended one. Most EMI noise induced in one lead is also induced in the other, the input only measures the difference between the two leads, and the EMI common to both is ignored. This effect is a major reason there is twisted pair wire as the twisting assures that both wires are subject to virtually identical external influ- ence. The diagram below shows a typical differential input configuration.

CH High

CH Low

LL GN D

I/O

Connector

+

Inp ut

 

To A /D

A m p

 

 

 

-

Differential Input

~

CH High

Vs

+

Inp ut

Vs

CH Low

Vcm

LL GND

A m p

-

To A/D

g1

Vcm = Vg2 - Vg1

g 2

Common Mode Voltage (Vcm) is ignored by differential input configuration. However, note that Vcm + Vs must remain within

the am plifier’s comm on mode range of ±10V

Diffe rential Inp ut

Before moving on to the discussion of grounding and isolation, it is important to explain the concepts of common mode, and common mode range (CM Range). Common mode voltage is depicted in the diagram above as Vcm. Though differential inputs measure the voltage between two signals, without (almost) respect to the either signal’s voltages relative to ground, there is a limit to how far away from ground either signal can go. Though the PCI-DAS1000 has differential inputs, it will not measure the difference between 100V and 101V as 1 Volt (in fact the 100V would destroy the board!). This limitation or common mode range is depicted graphically in the following diagram. The PCI-DAS1000 common mode range is +/- 10 Volts. Even in differential mode, no input signal can be measured if it is more than 10V from the board’s low level ground (LLGND).

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Contents Users Guide Table of Contents BADR2 BADR0 BADR1BADR3 BADR4Introduction Introduction InstallationDOS and/or Windows RUN InstaCalHardware Connections Connector PIN DiagramAnalog Connections Single-Ended and Differential InputsSingle-Ended Inputs Differential Inputs Differential InputWhich system do you have? System Grounds and IsolationSystems with Common Mode ground offset Voltages Small Common Mode VoltagesLarge Common Mode Voltages Ground Category Input Configuration Our view PCI-DAS1000 and signal source already have isolated grounds    Board Board Programming & Software Applications Analog Inputs SELF-CALIBRATION of the PCI-DAS1000Analog Outputs BADR1 BADR0Interrupt / ADC Fifo Register Region Function OperationsEoaie InteIntcl AdflclCHL8-CHL1, CHH8-CHH1 ADC Channel MUX and Control Register BADR1 +EOC Pacer Source= ADC Done = ADC Busy Trigger CONTROL/STATUS Register BADR1 + TS10ARM C0SRC Fifo Mode Sample CTRXtrig IndxgtBADR1 + Calibration RegisterDAC Channel Cal Function Cal SourceDAC CONTROL/STATUS Register BADR1 + Dacen ModeDACnR10 DACnR1 DACnR0 Range LSB SizeADC Data Register BADR2 + BADR2ADC Fifo Clear Register BADR2 + MSB LSBADC Pacer Clock Data and Control Registers BADR3BADR3 + Device Counter # FunctionDigital I/O Data and Control Registers ADC 8254 Control RegisterDIO Port a Data DIO Port B DataDIO Port C Data DIO Control RegisterPort a Port C Port B Upper Lower OUT 8254B Counter 1 Data User Counter #5 Index and User Counter 4 Data and Control Registers8254B Counter 2 Data User Counter #6 BADR3 + AhBADR3 + Bh 8254B Control Register1 DAC0 Data Register BADR4BADR4 + 2 DAC1 Data RegisterElectrical Specifications Analog Output Environmental Power consumptionEC Declaration of Conformity
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