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LM34CAH Fiches technique(PDF) 5 Page - National Semiconductor (TI) |
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LM34CAH Fiches technique(HTML) 5 Page - National Semiconductor (TI) |
5 / 10 page Typical Applications The LM34 can be applied easily in the same way as other integrated-circuit temperature sensors It can be glued or cemented to a surface and its temperature will be within about 002 F of the surface temperature This presumes that the ambient air temperature is almost the same as the surface temperature if the air temperature were much high- er or lower than the surface temperature the actual temper- ature of the LM34 die would be at an intermediate tempera- ture between the surface temperature and the air tempera- ture This is expecially true for the TO-92 plastic package where the copper leads are the principal thermal path to carry heat into the device so its temperature might be clos- er to the air temperature than to the surface temperature To minimize this problem be sure that the wiring to the LM34 as it leaves the device is held at the same tempera- ture as the surface of interest The easiest way to do this is to cover up these wires with a bead of epoxy which will insure that the leads and wires are all at the same tempera- ture as the surface and that the LM34 die’s temperature will not be affected by the air temperature The TO-46 metal package can also be soldered to a metal surface or pipe without damage Of course in that case the Vb terminal of the circuit will be grounded to that metal Alternatively the LM34 can be mounted inside a sealed-end metal tube and can then be dipped into a bath or screwed into a threaded hole in a tank As with any IC the LM34 and accompanying wiring and circuits must be kept insulated and dry to avoid leakage and corrosion This is especially true if the circuit may operate at cold temperatures where condensation can occur Printed-circuit coatings and var- nishes such as Humiseal and epoxy paints or dips are often used to insure that moisture cannot corrode the LM34 or its connections These devices are sometimes soldered to a small light- weight heat fin to decrease the thermal time constant and speed up the response in slowly-moving air On the other hand a small thermal mass may be added to the sensor to give the steadiest reading despite small deviations in the air temperature Capacitive Loads Like most micropower circuits the LM34 has a limited ability to drive heavy capacitive loads The LM34 by itself is able to drive 50 pF without special precautions If heavier loads are anticipated it is easy to isolate or decouple the load with a resistor see Figure 3 Or you can improve the tolerance of capacitance with a series R-C damper from output to ground see Figure 4 When the LM34 is applied with a 499X load resistor (as shown) it is relatively immune to wiring capacitance because the capacitance forms a bypass from ground to input not on the output However as with any linear circuit connected to wires in a hostile environ- ment its performance can be affected adversely by intense electromagnetic sources such as relays radio transmitters motors with arcing brushes SCR’s transients etc as its wiring can act as a receiving antenna and its internal junc- tions can act as rectifiers For best results in such cases a bypass capacitor from VIN to ground and a series R-C damper such as 75X in series with 02 or 1 mF from output to ground are often useful These are shown in the following circuits Temperature Sensor Single Supply b50 to a300 F TLH6685 – 6 TLH6685 – 7 FIGURE 3 LM34 with Decoupling from Capacitive Load TLH6685 – 8 FIGURE 4 LM34 with R-C Damper Temperature Rise of LM34 Due to Self-Heating (Thermal Resistance) Conditions TO-46 TO-46 TO-92 TO-92 SO-8 SO-8 No Heat Sink Small Heat Fin No Heat Sink Small Heat Fin No Heat Sink Small Heat Fin Still air 720 FW 180 FW 324 FW 252 FW 400 FW 200 FW Moving air 180 FW 72 FW 162 FW 126 FW 190 FW 160 FW Still oil 180 FW 72 FW 162 FW 126 FW Stirred oil 90 FW 54 FW 81 FW 72 FW (Clamped to metal (43 FW) (95 FW) infinite heat sink) Wakefield type 201 or 1 disc of 0020 sheet brass soldered to case or similar TO-92 and SO-8 packages glued and leads soldered to 1 square of printed circuit board with 2 oz copper foil or similar 5 |
Numéro de pièce similaire - LM34CAH |
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Description similaire - LM34CAH |
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