Omega OME-A822PG manual Analog Input Signal Connection

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2.9 Analog Input Signal Connection

The OME-A-822 can measure signals in the single-ended or differential mode. In the differential mode each channel has a unique signal HIGH and signal LOW connection. In the single-ended mode all channels have a unique signal HIGH connection but share a common LOW or ground connection. Differential connections are very useful for low level signals (millivolt), since they better reject electrical noise that can affect the quality of the measurement. A differential connection is also necessary when a common ground is unacceptable. The benefit of using a single-ended connection is that twice the number of channels is available. In general, a single-ended connection is often a good choice when working with higher level signals (5V or 10V for example), especially if the signal is coming from an isolated device such as a signal conditioner. Several different types of wiring diagrams are discussed below.

Figure 1-A shows a differential connection to a grounded source. If the source is grounded, making a second connection to the card’s ground could cause a ground loop resulting in erroneous data. It is important to note that the maximum common mode voltage between the input source and AGND is 70Vp-p. If the card is connected to a source with a common mode voltage greater than 70Vp-p, the input multiplexer will be permanently damaged! When measuring common mode voltage, it is best to use an oscilloscope rather than a multi-meter.

Figure 1-B shows a differential connection to a floating source. In such cases a connection should be made between the low channel input and analog ground.

Figure 2 shows connection of multiple sources in single-ended mode. This connection assumes creating one common ground will not cause a problem. This is normally the case when connecting to devices that are isolated or floating.

Figure 3 demonstrates how to connect bridge transducers. Bridge transducers include strain gauges, load cells and certain type of pressure transducers. The diagram assumes that there is a single external power supply providing power to the bridge. Each bridge is connected to a differential channel. No connection is made between channel low and analog ground. A connection should be made between analog ground and the negative of the power supply. An isolated power supply is strongly suggested.

Figure 4 demonstrates how to connect a 4-20mA current loop. Since the card reads voltages, the current is converted to voltage by passing it through a shunt resistor. By Ohms law (V=IR), when using a 250Ω resistor, 4 mA will be converted to 1V and 20mA to 5V. If the source is linear, the output voltage range will also be linear.

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Contents User’sGuide Benelux CanadaMexico Czech RepublicOME-A-822PGH/PGL Tables of Contents IntroductionConnector Features General DescriptionAnalog Inputs SpecificationsPower Consumption 3 A/D ConverterDigital I/O DA ConverterInterrupt Channel Programmable Timer/Counter Direct Memory Access Channel DMAApplications Product Check ListHardware Configuration Board LayoutI/O Base Address Setting Default base address isJumper Settings 1 JP1 D/A Internal Reference Voltage Selection2 JP2 D/A Int/Ext Ref Voltage Selection 3 JP3 Single-ended/Differential Selection4 JP4 A/D Trigger Source Selection 5 JP5 Interrupt Level Selection6 JP6 User Timer/Counter Clock Input Selection 7 JP7 DMA Dack Selection JP8 DMA DRQ Selection DRQ JP7 Dack JP8 DMAI/O Register Address Address Read Write2 A/D Input Buffer Register 1 8254 CounterConversion is completed, the Ready bit will clear to zero 3 D/A Output Latch Register 4 D/I Input Buffer Register Clear Interrupt Request6 A/D Gain Control Register GAIN3 GAIN2 GAIN1 GAIN0OME-A-822PGH Gain Control Code Table 7 A/D Multiplex Control Register8 A/D Mode Control Register 9 A/D Software Trigger Control Register 10 D/O Output Latch Register Digital I/O CN28254 Timer/Counter CounterA/D Conversion 1 A/D conversion flow Polling, interrupt and DMA2 A/D Conversion Trigger Modes 3 A/D Transfer ModesDelay the settling time refer to Sec .4.6 and Sec Using software trigger and polling transferRefer to Sec D/A Conversion Analog Input Signal Connection OME-A-822PGL/PGH Hardware Manual OME-A-822PGL/PGH Hardware Manual Signal Shielding Use a single connection to frame ground not A.GND or D.GNDUsing OME-DB-8225 CJC Output CN1 Digital Input Pin Assignment CN1/CN2/CN3 Pin AssignmentCN2 Digital Output Pin Assignment SINGLE-ENDED Signal Mode Differential Signals OME-DB-37 Daughter BoardOME-DB-8225 OME-DB-16PCalibration Description of Variable ResistorsD/A Calibration A/D Calibration Diagnostic Utility IntroductionOME-A-822PGL/PGH Hardware Manual Running The Diagnostic Utility Setup Base address selection screenDMA no and IRQ no selection screen Calibration Function Test Test Test Screen Digital I/O Test Screen Multiplexer Test Screen Use IRQ Test Screen Use DMA Test Screen DA Gain Test Screen Timer 0 Test Screen Special Test Help WARRANTY/DISCLAIMER Temperature
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