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AD597 bảng dữ liệu(PDF) 5 Page - Analog Devices |
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AD597 bảng dữ liệu(HTML) 5 Page - Analog Devices |
5 / 8 page AD596/AD597 REV. B –5– SETPOINT CONTROL MODE The AD596/AD597 can be connected as a setpoint controller as shown in Figure 2. The thermocouple voltage is cold junction compensated, amplified, and compared to an external setpoint voltage. The relationship between setpoint voltage and tempera- ture is given in Table I. If the temperature to be controlled is within the operating range (–55 °C to +125°C) of the device, it can monitor its own temperature by shorting the inputs to ground. The setpoint voltage with the thermocouple inputs grounded is given by the expressions: AD596 Setpoint Voltage = °C × 9.6 mV/°C + 42 mV AD597 Setpoint Voltage = °C × 10.1 mV/°C – 9.1 mV The input impedance of the setpoint pin of the AD596/AD597 is approximately 50 k Ω. The temperature coefficient of this resistance is ±15 ppm/°C. Therefore, the 100 ppm/°C 5 kΩ pot shown in Figure 2 will only introduce an additional ±1°C degra- dation of temperature stability over the +25 °C to +100°C ambi- ent temperature range. AD596/ AD597* CONSTANTAN (ALUMEL) IRON (CHROMEL) 0.01 F +V R HYSTERESIS (OPTIONAL) TEMPERATURE CONTROLLED REGION HEATER DRIVER TEMPERATURE COMPARATOR OUTPUT SET- POINT VOLTAGE VREF 5k 100ppm/ C SET- POINT VOLTAGE *H PACKAGE PINOUT SHOWN Figure 2. Setpoint Control Mode Switching hysteresis is often used in setpoint systems of this type to provide noise immunity and increase system reliability. By reducing the frequency of on-off cycling, mechanical component wear is reduced leading to enhanced system reliability. This can easily be implemented with a single external resistor between Pins 7 and 3 of the AD596/AD597. Each 200 nA of current injected into Pin 3 when the output switches will cause about 1 °C of hysteresis; that is: RHYST (Ω) = VOUT 200 nA × 1 °C HYST In the setpoint configuration, the AD596/AD597 output is saturated at all times, so the alarm transistor will be ON regard- less of whether there is an open circuit or not. However, –ALM must be tied to a voltage below (+VS – 4 V) for proper operation of the rest of the circuit. STAND-ALONE TEMPERATURE TRANSDUCER The AD596/AD597 may be configured as a stand-alone Celsius thermometer as shown in Figure 3. 0.01 F –VS VOUT 9.6mV/ C +VS 0.01 F + – G A + ICE POINT COMP + AD596/ AD597* + – G *H PACKAGE PINOUT SHOWN Figure 3. Stand-Alone Temperature Transducer Temperature Proportional Output Connection Simply omit the thermocouple and connect the inputs (Pins 1 and 2) to common. The output will now reflect the compensa- tion voltage and hence will indicate the AD596/AD597 tem- perature. In this three terminal, voltage output, temperature sensing mode, the AD596/AD597 will operate over the full extended –55 °C to +125°C temperature range. The output scaling will be 9.6 mV per °C with the AD596 and 10.1 mV per °C with the AD597. Additionally there will be a 42 mV offset with the AD596 causing it to read slightly high when used in this mode. THERMOCOUPLE CONNECTIONS The connection of the thermocouple wire and the normal wire or printed circuit board traces going to the AD596/AD597 forms an effective reference junction as shown in Figure 4. This junction must be kept at the same temperature as the AD596/ AD597 for the internal cold junction compensation to work properly. Unless the AD596/AD597 is in a thermally stable enclosure, the thermocouple leads should be brought in directly to Pins 1 and 2. REFERENCE JUNCTION CONSTANTAN (ALUMEL) IRON (CHROMEL) NOTE: A BIAS RETURN PATH FROM PINS 1 AND 2 OF LESS THAN 1k IMPEDANCE MUST BE PROVIDED. 0.01 F AD596/ AD597* LIMITING RESISTOR TO LED 0.01 F +VS VOUT *H PACKAGE PINOUT SHOWN GND –VS Figure 4. PCB Connections To ensure secure bonding, the thermocouple wire should be cleaned to remove oxidization prior to soldering. Noncorrosive resin flux is effective with iron, constantan, chromel, and alumel, and the following solders: 95% tin–5% silver, or 90% tin–10% lead. |
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