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LabJack U12 User Manual
Also see for U12: User guideQuick guideQuick start guide
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2.1 AI0 – AI7HardwareThe LabJack U12 has 8 screw terminals for analog input signals. These can be configuredindividually and on-the-fly as 8 single-ended channels, 4 differential channels, or combinationsin between. Each input has a 12-bit resolution and an input bias current of ±90 μA.• Single-Ended: The input range for a single-ended measurement is ±10 volts.• Differential channels can make use of the low noise precision PGA to provide gains upto 20, giving an effective resolution greater than 16-bits. In differential mode, the voltageof each AI with respect to ground must be between ±10 volts, but the range of voltagedifference between the 2 AI is a function of gain (G) as follows:G=1 ±20 voltsG=2 ±10 voltsG=4 ±5 voltsG=5 ±4 voltsG=8 ±2.5 voltsG=10 ±2 voltsG=16 ±1.25 voltsG=20 ±1 voltThe reason the range is ±20 volts at G=1 is that, for example, AI0 could be +10 volts and AI1could be -10 volts giving a difference of +20 volts, or AI0 could be -10 volts and AI1 could be+10 volts giving a difference of -20 volts.Figure 2-2 shows a typical single-ended connection measuring the voltage of a battery. Thissame measurement could also be performed with a differential connection to allow the use ofthe PGA. In general, any single-ended measurement can be performed using a differentialchannel by connecting the voltage to an even-numbered analog input, and grounding theassociated odd-numbered analog input (as shown by the dashed connection to AI1 in Figure 2-2).Figure 2-2. Single-ended measurement.Figure 2-3 shows a typical differential connection measuring the voltage across a current shunt.A differential connection is required when neither leg of the shunt is at ground potential. Makesure that the voltage of both AI0 an AI1 with respect to ground is within ±10 volts. For instance,if the source (Vs) shown in Figure 2-3 is 120 VAC, the difference between AI0 and AI1 might besmall, but the voltage from both AI0 and AI1 to ground will have a maximum value near 170volts, and will seriously damage the LabJack. |
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