LM Temperature Controller. June General Description. The LM is a highly accurate temperature measurement and or control system for use over a b 25 C to a 85 C tem- perature range Fabricated on a single monolithic chip it includes a temperature sensor a stable voltage reference and an operational amplifier. The output voltage of the LM is directly proportional to temperature in degrees Kelvin at 10 mV K Using the inter- nal op amp with external resistors any temperature scale factor is easily obtained By connecting the op amp as a comparator the output will switch as the temperature trans- verses the set-point making the device useful as an on-off temperature controller.
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Dt Sheet. Fabricated on a single monolithic chip, it includes a temperature sensor, a stable voltage reference and an operational amplifier. Using the internal op amp with external resistors any temperature scale factor is easily obtained.
By connecting the op amp as a comparator, the output will switch as the temperature transverses the set-point making the device useful as an on-off temperature controller. An active shunt regulator is connected across the power leads of the LM to provide a stable 6.
This allows the use of any power supply voltage with suitable external resistors. The input bias current is low and relatively constant with temperature, ensuring high accuracy when high source impedance is used. Further, the output collector can be returned to a voltage higher than 6. The LM uses the difference in emitter-base voltage of transistors operating at different current densities as the basic temperature sensitive element. Since this output depends only on transistor matching the same reliability and stability as present op amps can be expected.
In the epoxy package all electrical connections are made on one side of the device allowing the other 4 leads to be used for attaching the LM to the temperature souce.
Note 2: The output voltage applies to the basic thermometer configuration with the output and input terminals shorted and a load resistance of t 1. This is the feedback sense voltage and includes errors in both the sensor and op amp. This voltage is specified for the sensor in a rapidly stirred oil bath. The output is referred to V a. Note 3: The output leakage current is specified with t mV overdrive. Since this voltage changes with temperature, the voltage drive for turn-off changes and is defined as VOUT with output and input shorted b mV.
Application Hints media will conduct the heat from the sensor. Also, there are many small heat sinks designed for transistors which will improve heat transfer to the sensor from the surrounding medium. A small finned clip-on heat sink is quite effective in free-air.
It should be mentioned that the LM die is on the base of the package and therefore coupling to the base is preferable. The internal reference regulator provides a temperature stable voltage for offsetting the output or setting a comparison point in temperature controllers.
However, since this reference is at the same temperature as the sensor temperature, changes will also cause reference drift. For application where maximum accuracy is needed an external reference should be used. Of course, for fixed temperature controllers the internal reference is adequate. Although the LM is designed to be totally trouble-free, certain precautions should be taken to insure the best possible performance.
Nominal suggested operating current for the shunt regulator is 1. In free, still, air this raises the package temperature by about 1.
Although the regulator will operate at higher reverse currents and the output will drive loads up to 5. Therefore, the sensor should be operated at the lowest possible power level. SCR heating, by proper positioning, can preheat the sensor giving control anticipation as is presently used in many home thermostats.
Wire wound resistors will provide maximum temperature stability. As used herein: 1. Life support devices or systems are devices or systems which, a are intended for surgical implant into the body, or b support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Europe Fax: a49 85 86 Email: cnjwge tevm2. Tel: Fax: National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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