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AD654JRZ-REEL7 датащи(PDF) 7 Page - Analog Devices |
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AD654JRZ-REEL7 датащи(HTML) 7 Page - Analog Devices |
7 / 12 page AD654 REV. –7– TWO-WIRE TEMPERATURE-TO-FREQUENCY CONVERSION Figure 8 shows the AD654 in a two-wire temperature-to-frequency conversion scheme. The twisted pair transmission line serves the dual purpose of supplying power to the device and also carrying frequency data in the form of current modulation. The positive supply line is fed to the remote V/F through a 140 Ω resistor. This resistor is selected such that the quiescent current of the AD654 will cause less than one VBE to be dropped. As the V/F oscillates, additional switched current is drawn through RL when Pin 1 goes low. The peak level of this additional cur- rent causes Q1 to saturate, and thus regenerates the AD654’s output square wave at the collector. The supply voltage to the AD654 then consists of a dc level, less the resistive line drop, plus a one VBE p-p square wave at the output frequency of the AD654. This ripple is reduced by the diode/capacitor combination. To set up the receiver circuit for a given voltage, the RS and RL resistances are selected as shown in Table I. CMOS logic stages can be driven directly from the collector of Q1, and a single TTL load can be driven from the junction of RS and R6. Table I. +VS RS ( )RL ( ) 10 V 270 1.8k 15 V 680 2.7k Table II. (+VS) R1 ( ) R2 ( ) R3 ( ) R4 ( ) R5 ( ) K 10 V – – – 100k 127k F = 10 Hz/K 15 V – – – 100k 127k °C 10 V 6.49k 4.02k 1k 95.3k 22.6k F = 10 Hz/ °C 15 V 12.7k 4.02k 1k 78.7k 36.5k °F 10 V 6.49k 4.42k 1k 154k 22.6k F = 5.55 Hz/ °F 15 V 12.7k 4.42k 1k 105k 36.5k At the V/F end, the AD592C temperature transducer is inter- faced with the AD654 in such a manner that the AD654 output frequency is proportional to temperature. The output frequency can be sealed and offset from K to °C or °F using the resistor values shown in Table II. Since temperature is the parameter of interest, an NPO ceramic capacitor is used as the timing capaci- tor for low V/F TC. When scaling per K, resistors R1–R3 and the AD589 voltage reference are not used. The AD592 produces a 1 µA/K current output which drives Pin 3 of the AD654. With the timing capacitor of 0.01 µF this produces an output frequency scaled to 10 Hz/K. When scaling per °C and °F, the AD589 and resistors R1–R3 offset the drive current at Pin 3 by 273.2 µA for scaling per °C and 255.42 µA for scaling per °F. This will result in fre- quencies sealed at 10 Hz/ °C and 5.55 Hz/°F, respectively. OPTOISOLATOR COUPLING A popular method of isolated signal coupling is via optoelec- tronic isolators, or optocouplers. In this type of device, the signal is coupled from an input LED to an output photo-transistor, with light as the connecting medium. This technique allows dc to be transmitted, is extremely useful in overcoming ground loop problems between equipment, and is applicable over a wide range of speeds and power. Figure 9 shows a general purpose isolated V/F circuit using a low cost 4N37 optoisolator. A +5 V power supply is assumed for both the isolated (+5 V isolated) and local (+5 V local) supplies. The input LED of the isolator is driven from the collector out- put of the AD654, with a 9 mA current level established by R1 for high speed, as well as for a 100% current transfer ratio. 5V (ISOLATED) R1 390 4N37 OPTO-ISOLATOR 5V (LOCAL) GRN LED OSC/ DRIVER RT 1k VIN (0V TO 1V) CT 1000pF AD654 R3 270 74LS14 Q1 2N3904 R2 120 V/F OUTPUT FS = 100kHz TTL ISOLATED LOCAL Figure 9. Optoisolator Interface OSC/ DRIVER AD654 VS (10V TO 15V) CT 0.01 F f = IT (10V) CT RT 1 F 1N4148 R4 R5 R1 R2 R3 + – AD589 AD592 140 RS R6 220 Q1 2N3906 CMOS OUTPUT TTL OUTPUT (1 LOAD) 1 A/k Figure 8. Two-Wire Temperature-to-Frequency Converter C |
Аналогичный номер детали - AD654JRZ-REEL7 |
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Аналогичное описание - AD654JRZ-REEL7 |
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