外文翻譯---降低測(cè)量噪聲的五個(gè)技巧-文庫(kù)吧資料
2025-01-24 00:02本頁(yè)面
【正文】 reads the resulting 5 V difference between the two terminals.Figure 1 An ideal instrumentation amplifier pletely rejects monmode voltages.The maximum working voltage of a data acquisition (DAQ) device refers to the signal voltage plus the monmode voltage and specifies the largest potential that may exist between an input and earth ground. The maximum working voltage for most DAQ devices is the same as the input range of the instrumentation amplifier. For example, lowcost M Series DAQ devices such as the NI 6220 devices have a maximum working voltage of 11 V。 no input signal can exceed 11 V without causing damage to the amplifier.Isolation can dramatically increase the maximum working voltage of a DAQ device. In the context of a measurement system, “isolation” means physically and electrically separating two parts of a circuit. An isolator passes data from one part of the circuit to another without conducting electricity. Because current cannot flow across this isolation barrier, you can levelshift the DAQ device ground reference away from earth ground. This decouples the maximum working voltage specification from the input range of the amplifier. For example, in Figure 2 the instrumentation amplifier ground reference is electrically isolated from earth ground.Figure 2 Isolation electrically separates the instrumentation amplifier ground reference from earth ground.While the input range is the same as that in Figure 1, the working voltage has been extended to 60 V, rejecting 55 V of monmode voltage. The maximum working voltage is now defined by the isolation circuitry instead of the amplifier input range.Fuel cell testing is an example application that requires high DC monmode voltage rejection. Each individual cell may generate approximately 1 V, but a stack of cells may produce several kilovolts or more. To accurately measure the voltage of a single 1 V cell, the measurement device must be able to reject the high monmode voltages generated by the rest of the stack.14 B. Reject AC CommonMode VoltageRarely do monmode voltages consist of only a DC level. Most sources of monmode voltage contain an AC ponent in addition to a DC offset. Noise is inevitably coupled onto a measured signal from the surrounding electromagnetic environment. This is particularly troublesome for lowlevel analog signals passing through the instrumentation amplifier on a DAQ device.Sources of AC noise may be broadly classified by their coupling mechanisms – capacitive, inductive, or radiative. Capacitive coupling results from timevarying electric fields, such as those created by nearby relays or other measurement signals. Inductive or magnetically coupled noise results from timevarying magnetic fields, such as those created by nearby machinery or motors. If the electromagnetic field source is far from the measurement circuit, such as with fluorescent lighting, the electric and magnetic field coupling is considered bined electromagnetic or radiative coupling. In all cases, a timevarying monmode voltage is coupled onto the signal of interest, most often in the range of 5060 Hz (powerline frequency).An ideal measurement circuit has a perfectly balanced path to both the positive and negative terminals of an instrumentation amplifier. Suc
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