Each additional table entry adds VR/8 to the total voltage. Or, put another way, the output voltage is equal to the binary, numeric value of S0–S2, times VR/8. This 3- switch DAC has 8 possible states and each voltage step is VR/8. We could add another R/2R pair and another switch to the circuit, making a 4-switch circuit with 16 steps of VR/16 volts each. An 8-switch circuit would have 256 steps of VR/256 volts each. Finally, we can replace the mechan- ical switches in the schematic with electronic switches to make a true DAC. Analog-to-Digital Converters The usual method of bringing analog inputs into a microprocessor is to use an analog-to-digital converter (ADC). An ADC accepts an analog input, a voltage or a current, and converts it to a digital word that can be read by a microprocessor. Figure 2.2 shows a simple ADC. This hypothetical part has two inputs: a reference and the signal to be measured. It has one output,
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Some offal is frozen in plate freezers. tially a less controlled process where only the Small processed items are typically frozen in surface is frozen. In tempering, product is continuous belt freezers or in cryogenic semifrozen so that it is stiff enough to be tunnels. sliced, cubed, etc. without deformation. Crust freezing and tempering are increas- Reducing deformation during cutting im- ingly being used to allow high-speed mechan- proves the yield, by enabling faster cutting ical portioning or slicing of meat and meat and reducing the number of misshapen slices. products. The final temperature distribution However, the process must be carefully con- produced by the freezing system is critical in trolled. The optimum tempering temperature such operations. is a function of the meat and the slicer. If too Although a great deal has been written on
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