4 bme325 experiment 4

8/10/2019 4 BME325 Experiment 4

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BME 325

MEDICAL ELECTRONICS

OPAMP APPLICATION US!NG LM335-SEMICONDUCTOR

TEMPERATURE SENSOR

1

EXPERIMENT 04

OPAMP APPLICATION USING LM335-SEMICONDUCTORTEMPERATURE SENSOR

Objective:

The aim of this experiment is the realization of a celcius thermometer using Lm335 series

semicondutor temperature sensor and measuring various temperatures, comparing the results

intended. Sensor output voltage must be set to show c unit on the screen of the multimeter

using opamp circuits (amplifiers and adder, and so on).

Theory:

LM335 is a precision, easily calibrated, integrated circuit temperature sensor with an

operating range of -40oC to 100oC. The low impedance and linear output makes interfacing toa control circuit simple. The sensor comes in a TO-92 package and provides an output voltagedirectly proportional to the absolute temperature at the rate of +10mV/oK. The output is

calibrated with an external potentiometer to provide a 2.98 V output at 25oC. When calibrated

at 25oC, the LM335 has an error of less than 1

oC over a 100

oC range. Output at ant

temperature can be calculated using the formula below

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Knowing output voltage at a reference temperature output voltage at any temperature is

calculated using equation. For example at 40C output of the LM335 is 3.13Volts. Then the

output at 100C is given byV (100) = V (40) (273+100) / (273+40) = 3.13 x 1.19

= 3.724 Volts.

Preliminary Work:

1) Calculate LM335 output at 20,25,30,35 C

Figure 1


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BME 325

MEDICAL ELECTRONICS


TEMPERATURE SENSOR

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2)

In the figure a dc power source V2 is used instead of LM335 and it is output is 3.03V.

output of U1,U2 and U3 are indicated. Calculate the unknown values for the circuit in

figure 1 (including V3 DC source) so that the output voltage of the circuit will be

equal to temperature in C but in mVs. For example at 40C output of the LM335 is

approximately 3.13Volts or at 45C output of the LM335 is approximately 3.18Volts

but the circuit output measured by a multimeter must be 40mV, and 45mV

respectively. (for further information inspect LM335 datasheet).

!!! ANYBODY WHO DID NOT PREPARE PRELIMINARY WORK CAN NOT JOIN THE EXPERIMENT !!!

Procedure:

1) Calibrate LM335 as defined below.

Output voltage change per degree change in temperature is known as temperaturesensitivity. LM335 is designed for 10mV/C. This makes it an ultra sensitive

temperature sensor. STS(semiconductor Tempereture Sensor) is biased using a

regulated power supply. The biasing current is within 400A to 5mA for LM335 and

family. Figure 2 shows a STS biased using a dc power supply. A series resistor limits

current (1.6mA) within the prescribed range. (If you want to use a single DC power

source for the positive voltage values for the whole circuit calculate the resistor value

that must be used instead of 5.6k)

Figure 2 Pin Connection Lm335 Figure 3

STS output is calibrated to read exact temperature in degree Kelvin using a potentiometer asshown in Figure 2. In this calibration process the wiper of the potentiometer is connected to

the adjustment terminal. Once calibrated at one temperature the potentiometer is undisturbed.

2) Construct the circuit in figure 3. For accurate results you are advised to use

potentiometers so that you can adjust accurately.

- + Adj.

VoTP1

10KLM3359V

5.6K


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BME 325

MEDICAL ELECTRONICS


TEMPERATURE SENSOR

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3) Measure different temperetures in a range as wide as possible, compare your results

with a thermometer afill the table below and draw temrepereture vs. volts diagram for

the thermometer,sensor and circuit output.

Fill the report by necessary measured values and graphs

Question:

Explain the use and purpose of each opamp.

Equipment List:

3 741 Opamp

6 x 10 k , 1x5,6k, 1 x 1 k resistor, 3 x 10 k potentiometer

1 piece LM335 temperature sensor

Multimeter

Power supply (+15V,-15V,+9V,+5V)


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BME 325

MEDICAL ELECTRONICS


TEMPERATURE SENSOR

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REPORT:

1.

Tempereture (C)Sensor Output (V)

Circuit Output

(V0)Measured Calculated

2. (C)

3. Answer of the Question

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Student ID # :

Name :

V3:

4 bme325 experiment 4

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