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AD597 数据表(PDF) 4 Page - Analog Devices |
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AD597 数据表(HTML) 4 Page - Analog Devices |
4 / 8 page AD596/AD597 REV. B –4– TEMPERATURE PROPORTIONAL OUTPUT MODE The AD596/AD597 can be used to generate a temperature proportional output of 10 mV/ °C when operated with J and K type thermocouples as shown in Figure 1. Thermocouples pro- duce low level output voltages which are a function of both the temperature being measured and the reference or cold junction temperature. The AD596/AD597 compensates for the cold junction temperature and amplifies the thermocouple signal to produce a high level 10 mV/ °C voltage output which is a func- tion only of the temperature being measured. The temperature stability of the part indicates the sensitivity of the output voltage to changes in ambient or device temperatures. This is typically 0.02 °C/°C over the +25°C to +100°C recommended ambient temperature range. The parts will operate over the extended ambient temperature ranges from –55 °C to +125°C, but ther- mocouple nonlinearity at the reference junction will degrade the temperature stability over this extended range. Table I is a list of ideal AD596/AD597 output voltages as a function of Celsius temperature for type J and K ANSI standard thermocouples with package and reference junction at 60 °C. As is normally the case, these outputs are subject to calibration and temperature sensitivity errors. These tables are derived using the ideal trans- fer functions: AD596 output = (Type J voltage + 301.5 µV) × 180.57 AD597 output = (Type K voltage) × 245.46 0.01 F 1M +15V –15V 100k 10k 100k CONSTANTAN (ALUMEL) IRON (CHROMEL) OPTIONAL OFFSET ADJUST 0.01 F VOUT +5V TO +30V 0 TO –25V SPAN OF +5V TO +30V AD596/ AD597* *H PACKAGE PINOUT SHOWN Figure 1. Temperature Proportional Output Connection The offsets and gains of these devices have been laser trimmed to closely approximate thermocouple characteristics over mea- surement temperature ranges centered around 175 °C with the AD596/AD597 at an ambient temperature between 25 °C and 100 °C. This eliminates the need for additional gain or offset adjustments to make the output voltage read: VOUT = 10 mV/ °C × (thermocouple temperature in °C) (within specified tolerances). Excluding calibration errors, the above transfer function is accu- rate to within 1 °C from +80°C to +550°C for the AD596 and –20 °C to +350°C for the AD597. The different temperature ranges are due to the differences in J and K type thermocouple curves. European DIN FE-CuNi thermocouple vary slightly from ANSI type J thermocouples. Table I does not apply when these types of thermocouples are used. The transfer functions given previ- ously and a thermocouple table should be used instead. Figure 1 also shows an optional trimming network which can be used to change the device’s offset voltage. Injecting or sinking 200 nA from Pin 3 will offset the output approximately 10 mV (1 °C). The AD596/AD597 can operate from a single supply from 5 V to 36 V or from split supplies totalling 36 V or less as shown. Since the output can only swing to within 2 V of the positive supply, the usable measurement temperature range will be re- stricted when positive supplies less than 15 V for the AD597 and 10 V for the AD596 are used. If the AD596/AD597 is to be used to indicate negative Celsius temperatures, then a negative supply is required. Common-mode voltages on the thermocouple inputs must remain within the common-mode voltage range of the AD596/ AD597, with a return path provided for the bias currents. If the thermocouple is not remotely grounded, then the dotted line connection shown in Figure 1 must be made to one of the ther- mocouple inputs. If there is no return path for the bias currents, the input stage will saturate, causing erroneous output voltages. In this configuration, the AD596/AD597 H package option has circuitry which detects the presence of an open thermocouple. If the thermocouple loop becomes open, one or both of the inputs to the device will be deprived of bias current causing the output to saturate. It is this saturation which is detected internally and used to activate the alarm circuitry. The output of this feature has a flexible format which can be used to source or sink up to 20 mA of current. The collector (+ALM) should not be allowed to become more positive than (–VS + 36 V), however, it may be permitted to be more positive than +VS. The emitter voltage (–ALM) should be constrained such that it does not become more positive than 4 V below +VS. If the alarm feature is not used, this pin should be connected to Pins 4 or 5 as shown in Figure 1. The alarm function is unavailable on the AR package option. |
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类似说明 - AD597 |
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