データシートサーチシステム |
|
AD595CDZ データシート(PDF) 5 Page - Analog Devices |
|
AD595CDZ データシート(HTML) 5 Page - Analog Devices |
5 / 8 page AD594/AD595 REV. C –5– The AD594/AD595 also includes an input open circuit detector that switches on an alarm transistor. This transistor is actually a current-limited output buffer, but can be used up to the limit as a switch transistor for either pull-up or pull-down operation of external alarms. The ice point compensation network has voltages available with positive and negative temperature coefficients. These voltages may be used with external resistors to modify the ice point com- pensation and recalibrate the AD594/AD595 as described in the next column. The feedback resistor is separately pinned out so that its value can be padded with a series resistor, or replaced with an external resistor between Pins 5 and 9. External availability of the feedback resistor allows gain to be adjusted, and also permits the AD594/ AD595 to operate in a switching mode for setpoint operation. CAUTIONS: The temperature compensation terminals (+C and –C) at Pins 2 and 6 are provided to supply small calibration currents only. The AD594/AD595 may be permanently damaged if they are grounded or connected to a low impedance. The AD594/AD595 is internally frequency compensated for feed- back ratios (corresponding to normal signal gain) of 75 or more. If a lower gain is desired, additional frequency compensation should be added in the form of a 300 pF capacitor from Pin 10 to the output at Pin 9. As shown in Figure 5 an additional 0.01 µF capacitor between Pins 10 and 11 is recommended. AD594/ AD595 VO COMP +V 9 10 11 300pF 0.01 F Figure 5. Low Gain Frequency Compensation RECALIBRATION PRINCIPLES AND LIMITATIONS The ice point compensation network of the AD594/AD595 produces a differential signal which is zero at 0 °C and corre- sponds to the output of an ice referenced thermocouple at the temperature of the chip. The positive TC output of the circuit is proportional to Kelvin temperature and appears as a voltage at +T. It is possible to decrease this signal by loading it with a resistor from +T to COM, or increase it with a pull-up resistor from +T to the larger positive TC voltage at +C. Note that adjustments to +T should be made by measuring the voltage which tracks it at –T. To avoid destabilizing the feedback amplifier the measuring instrument should be isolated by a few thousand ohms in series with the lead connected to –T. AD594/ AD595 +IN –IN +T COM –T FB VO 9 1 14 8 3 4 5 Figure 6. Decreased Sensitivity Adjustment Changing the positive TC half of the differential output of the compensation scheme shifts the zero point away from 0 °C. The zero can be restored by adjusting the current flow into the nega- tive input of the feedback amplifier, the –T pin. A current into this terminal can be produced with a resistor between –C and –T to balance an increase in +T, or a resistor from –T to COM to offset a decrease in +T. If the compensation is adjusted substantially to accommodate a different thermocouple type, its effect on the final output volt- age will increase or decrease in proportion. To restore the nominal output to 10 mV/ °C the gain may be adjusted to match the new compensation and thermocouple input characteristics. When reducing the compensation the resistance between –T and COM automatically increases the gain to within 0.5% of the correct value. If a smaller gain is required, however, the nominal 47 k Ω internal feedback resistor can be paralleled or replaced with an external resistor. Fine calibration adjustments will require temperature response measurements of individual devices to assure accuracy. Major reconfigurations for other thermocouple types can be achieved without seriously compromising initial calibration accuracy, so long as the procedure is done at a fixed temperature using the factory calibration as a reference. It should be noted that inter- mediate recalibration conditions may require the use of a negative supply. EXAMPLE: TYPE E RECALIBRATION—AD594/AD595 Both the AD594 and AD595 can be configured to condition the output of a type E (chromel-constantan) thermocouple. Tem- perature characteristics of type E thermocouples differ less from type J, than from type K, therefore the AD594 is preferred for recalibration. While maintaining the device at a constant temperature follow the recalibration steps given here. First, measure the device temperature by tying both inputs to common (or a selected common-mode potential) and connecting FB to VO. The AD594 is now in the stand alone Celsius thermometer mode. For this example assume the ambient is 24 °C and the initial output VO is 240 mV. Check the output at VO to verify that it corresponds to the temperature of the device. Next, measure the voltage –T at Pin 5 with a high impedance DVM (capacitance should be isolated by a few thousand ohms of resistance at the measured terminals). At 24 °C the –T voltage will be about 8.3 mV. To adjust the compensation of an AD594 to a type E thermocouple a resistor, R1, should be connected between +T and +C, Pins 2 and 3, to raise the voltage at –T by the ratio of thermocouple sensitivities. The ratio for converting a type J device to a type E characteristic is: r (AD594) =(60.9 µV/°C)/(51.7 µV/°C)= 1.18 Thus, multiply the initial voltage measured at –T by r and ex- perimentally determine the R1 value required to raise –T to that level. For the example the new –T voltage should be about 9.8 mV. The resistance value should be approximately 1.8 k Ω. The zero differential point must now be shifted back to 0 °C. This is accomplished by multiplying the original output voltage VO by r and adjusting the measured output voltage to this value by experimentally adding a resistor, R2, between –C and –T, Pins 5 and 6. The target output value in this case should be about 283 mV. The resistance value of R2 should be approxi- mately 240 k Ω. Finally, the gain must be recalibrated such that the output VO indicates the device’s temperature once again. Do this by adding a third resistor, R3, between FB and –T, Pins 8 and 5. VO should now be back to the initial 240 mV reading. The resistance value |
同様の部品番号 - AD595CDZ |
|
同様の説明 - AD595CDZ |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |