Omega Engineering OM-DAQ-USB-2401 manual Noise Reduction in Differential Mode

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Signal Management 5

Differential mode refers to a mode, or circuit set-up, in which a voltage is measured between two signal lines. The measured differential voltage is used for a single channel. An advantage of using differential inputs is that they reduce signal errors and the induction of noise resulting from ground current. The following illustration is an example of how noise is reduced, or canceled-out, when using the differential

Figure 5-3. Noise Reduction in Differential Mode

In the schematic, voltage signal S2 is subtracted from signal S1, resulting in the output signal shown. The noise spikes (having the same polarity, phase, and magnitude in each input signal) cancel each other out. This results in a clean differential signal (S1 - S2).

Floating-differential measurements are made when low-level signals must be measured in the presence of high levels of common-mode noise (e.g., a non- grounded thermocouple). When the signal source has no direct connection to the system analog common, one must be provided. In Omega Daq the connection to analog common is provided in the circuitry with both the channel high and channel low connected to analog common. Both of these connections to common are made through 1 MΩ resistors. No additional connections of channel high and low to common should be made.

Figure 5-4. Example of Floating Differential Circuit

NOTE:

Differential signal hookups do not provide isolation or any kind of circuit protection.

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Contents OM-DAQ-USB-2401 Servicing North America OM-DAQ-USB-2400 Multiple Channel USB Data Acquisition Module International Usage and CE Marking 10-1 OM-DAQ-USB-2400Section List of FiguresExamples of Under Sampling Introduction PrecautionsGeneral Description & System Components Safety Warnings and IEC SymbolsStatement on CE Marking System Components Included Items HardwarePackage Inspection OM-DAQ-USB-2401 System Components Hardware SetupUSB Hubs and Power Adaptors Power Adaptors USB-powered HubsSelf-powered Hubs Connecting Your OM-DAQ-USB-2401 Acquisition System to PC Direct Connection to Computer USB Ports Connecting Various Hardware SetupsConnections to Self-Powered and USB-powered Hubs Connection to USB-powered HubOM-DAQ-USB-2401 Mounting Connections to Self-Powered Hub and to USB-Powered HubOM-DAQ-USB-2400 Series OM-DAQ-USB-2401 Wall MountingOM-DAQ-USB-2401 Rail Mounting OM-DAQ-USB-2401 DIN Rail MountingSoftware Software InstallationGetting Started System RequirementsWelcome Screen Software SetupConfirm Installation Screen Main Control Window DAQ Central Software OperationToolbar Buttons Toolbar ButtonsFile Menu Main Control Window Pull-Down OperationsTools Menu Channels Tab 2 Device ConfigurationConfiguration Parameter Settings Manual Acquisition is manually started/stopped Level Data Displays Data Tab18. Main Window Screen 23. Waveform Screen A/D Conversion Power Line RejectionOptical Isolation Input Ranges Analog Input ConfigurationMeasurement Duration, Scan Time, and Resolution 27. Calibration/Scan Arrangement Automatic CalibrationThermocouple Measurements 28. Thermocouple WiringScan Time and Resolution Signal ManagementResolution Effective Number of Bits ENOB, RMS Channel Control and ExpansionRMS Under Sampling and AliasingExamples of Under Sampling SignalTriggering Signal ModesNoise Reduction in Differential Mode Analog Filtering System NoiseAveraging Crosstalk Input and Source ImpedanceVadc = VT x Ri / Rs + Ri = RCOM-DAQ-USB-2401 Design for CE Conformity CE ConformityFerrite Core Symptoms and Solutions TroubleshootingBasic Checklist Service & Calibration Service & CalibrationSpecifications External Power Source Power SupplyThermocouple Input Range Cold JunctionTC Type Temp Typical Fast Slow Thermocouple Accuracy ºC for OM-DAQ-USB-2401International Usage & CE Marking Approvals and Regulatory Compliance10-2 10-3 10-4 WARRANTY/DISCLAIMER Temperature