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AD592 Arkusz danych(PDF) 6 Page - Analog Devices |
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AD592 Arkusz danych(HTML) 6 Page - Analog Devices |
6 / 8 page AD592 REV. A –6– VT AVG (1mV/K) AD592 +5V 333.3 Ω (0.1%) VT AVG (10mV/K) 10k Ω (0.1%) +15V AD592 AD592 AD592 Figure 9. Average and Minimum Temperature Connections The circuit of Figure 10 demonstrates a method in which a voltage output can be derived in a differential temperature measurement. R1 50k Ω 10k Ω AD741 VOUT = (T1 – T2) x (10mV/oC) 10k Ω 5M Ω –V +V AD592 AD592 Figure 10. Differential Measurements R1 can be used to trim out the inherent offset between the two devices. By increasing the gain resistor (10 k Ω) temperature measurements can be made with higher resolution. If the magni- tude of V+ and V– is not the same, the difference in power con- sumption between the two devices can cause a differential self-heating error. Cold junction compensation (CJC) used in thermocouple signal conditioning can be implemented using an AD592 in the circuit configuration of Figure 11. Expensive simulated ice baths or hard to trim, inaccurate bridge circuits are no longer required. AD OP07E REFERENCE JUNCTION 100k Ω 10k Ω VOUT +7.5V MEASURING JUNCTION 1k Ω AD592 R THERMOCOUPLE TYPE APPROX. R VALUE J K T E S R 52 Ω 41 Ω 41 Ω 61 Ω 6 Ω 6 Ω 2.5V AD1403 RG1 RG2 (1k Ω) Cu Cu Figure 11. Thermocouple Cold Junction Compensation Response of the AD592 output to abrupt changes in ambient temperature can be modeled by a single time constant τ expo- nential function. Figure 8 shows typical response time plots for several media of interest. TIME – sec 100 80 60 50 40 30 20 10 90 70 A B C D E F 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 A ALUMINUM BLOCK B FLUORINERT LIQUID C MOVING AIR (WITH HEAT SINK) D MOVING AIR (WITHOUT HEAT SINK) E STILL AIR (WITH HEAT SINK) F STILL AIR (WITHOUT HEAT SINK) Figure 8. Thermal Response Curves The time constant, τ, is dependent on θ JA and the thermal ca- pacities of the chip and the package. Table I lists the effective τ (time to reach 63.2% of the final value) for several different media. Copper printed circuit board connections where ne- glected in the analysis, however, they will sink or conduct heat directly through the AD592’s solder dipped Kovar leads. When faster response is required a thermally conductive grease or glue between the AD592 and the surface temperature being mea- sured should be used. In free air applications a clip-on heat sink will decrease output stabilization time by 10-20%. MOUNTING CONSIDERATIONS If the AD592 is thermally attached and properly protected, it can be used in any temperature measuring situation where the maximum range of temperatures encountered is between –25 °C and +105 °C. Because plastic IC packaging technology is em- ployed, excessive mechanical stress must be safeguarded against when fastening the device with a clamp or screw-on heat tab. Thermally conductive epoxy or glue is recommended under typical mounting conditions. In wet or corrosive environments, any electrically isolated metal or ceramic well can be used to shield the AD592. Condensation at cold temperatures can cause leakage current related errors and should be avoided by sealing the device in nonconductive epoxy paint or dips. APPLICATIONS Connecting several AD592 devices in parallel adds the currents through them and produces a reading proportional to the aver- age temperature. Series AD592s will indicate the lowest tem- perature because the coldest device limits the series current flowing through the sensors. Both of these circuits are depicted in Figure 9. |
Podobny numer części - AD592_15 |
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Podobny opis - AD592_15 |
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