Exercise 2: Introduction to the Circuit Board Manual 28 FACET by Lab-Volt Familiarization Transducer Fundamentals Exercise 2: Introduction to the Circuit Board EXERCISE OBJECTIVE When

Student Manual

28 FACET by Lab-Volt

Familiarization Transducer Fundamentals

Exercise 2: Introduction to the Circuit Board

EXERCISE OBJECTIVE

When you have completed this exercise, you will be able to locate and describe the operation of the

various circuit blocks on your TRANSDUCER FUNDAMENTALS circuit board. You will verify your results

by making interconnections and taking measurements.

DISCUSSION

The TRANSDUCER FUNDAMENTALS circuit board contains 8 transducer circuit blocks, each of which is

The 8 transducer blocks are:

1. IC TRANSDUCER

2. THERMISTOR

3. RTD

4. THERMOCOUPLE

5. STRAIN GAUGE

6. CAPACITANCE SENSOR

7. ULTRASONIC TRANSDUCERS

8. INFRARED CONTROLLER

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FACET by Lab-Volt 29

Transducer Fundamentals Familiarization

There are also three auxiliary circuit blocks needed for the operation of the transducer circuitry.

The auxiliary blocks are:

1. REFERENCE SUPPLY

2. INSTRUMENTATION AMPLIFIER

3. OVEN

Which of these auxiliary blocks has jacks that allow you to connect to other circuit blocks with patch

leads?

a. REFERENCE SUPPLY

b. INSTRUMENTATION AMPLIFIER

c. OVEN

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The REFERENCE SUPPLY circuit block converts the + and –15 Vdc from your FACET base unit to

–5 Vdc and + and –0.5 Vdc.

J1 is a 20-pin dual-row header that you can use to interface the TRANSDUCER FUNDAMENTALS circuit

board with the FACET 32-BIT MICROPROCESSOR circuit board.

This connection and an optional unit in this volume allow you to demonstrate computerized measurement

and control of transducer circuitry to simulate automated systems.

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noise.

The INSTRUMENTATION AMPLIFIER circuit block on your circuit board can be used to amplify signals

from several of the transducer circuit blocks.

a. two

b. three

c. four

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You should place the switch for the desired gain in the up position, and only one switch should be up at

any time.

for making connections.

The third auxiliary circuit block is the OVEN. The oven components are enclosed in a clear plastic cover

to create a sealed, controlled air space for experiments involving temperature.

The eight resistors are wired in series and are used as a heating element. Each resistor is 8.2 , 0.5 W.

What are the equivalent resistance and power ratings of the series combination?

a. 8.2 , 4 W

b. 1.025 , 4 W

c. 65.6 , 4 W

d. 65.6 , 0.5 W

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Four of the transducer circuit blocks (IC TRANSDUCER, THERMISTOR, THERMOCOUPLE, and RTD)

contain temperature transducer circuitry. However, the transducers themselves are physically located

inside the oven, where they sense the heat generated by the resistors.

One of the temperature transducer blocks is used as an oven controller to regulate the oven temperature.

This block has a two-post connector position labeled “OVEN ENABLE.”

Which temperature transducer block is used as an oven controller?

a. IC TRANSDUCER

b. THERMISTOR

c. RTD

d. THERMOCOUPLE

Performing procedures involving temperature measurement and control are more easily accomplished by

heating the enclosed air space in the oven, avoiding dependence on ambient (surrounding) temperatures,

which can vary greatly.

There are four types of temperature transducers used on your circuit board. These are the IC transducer,

thermistor, RTD, and thermocouple.

Each type has different properties and characteristics that are used to determine its suitability to a

particular application.

Properties to be considered include output type, operating range, linearity, stability, and cost.

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operation. You can see that some of the temperature transducer blocks have potentiometers for you to

make the adjustments.

Which temperature transducer block does not have a pot?

a. IC TRANSDUCER

b. THERMISTOR

c. RTD

d. THERMOCOUPLE

A strain gauge is a transducer that measures the strain on the surface of the object to which it is attached.

In the STRAIN GAUGE circuit block on your circuit board, the transducer is mounted to a thin metal beam

According to the schematic symbol of the strain gauge, what type of output does this transducer have?

a. voltage

b. current

c. resistive

d. capacitive

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touch sensor, proximity detector, position sensor, and displacement measuring device.

The capacitance sensor is an example of a transducer that converts a mechanical motion into an

electrical signal.

circuit board.

The movable plate is above the circuit board and slides forward and back between a set of parallel

guides.

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As you slide the movable plate from bottom to top, the capacitance increases linearly from a minimum to

a maximum value.

maximum displacement from the 0 cm mark?

a. 0 cm

b. 1 cm

c. 3 cm

d. 3 inches

The ULTRASONIC TRANSDUCERS circuit block has separate TRANSMITTER and RECEIVER sections.

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There are two ultrasonic transducers. One is used as a transmitter (T) and the other as a receiver (R).

Ultrasonic transducers can be used to measure distance. The transmitter emits ultrasonic pulses that

strike a nearby object and echo back to the receiver.

By measuring the time it takes for the pulse to echo back from an object, you can accurately calculate the

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The INFRARED CONTROLLER circuit block uses infrared light to send and receive digital codes. A

familiar application of this technology is the wireless remote control used with TVs, VCRs, and stereos.

The INFRARED CONTROLLER circuit block has separate RECEIVER and TRANSMITTER sections.

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In the TRANSMITTER section, you can set a 4-bit binary code on the DIP switches.

The parallel data is converted into serial data and is transmitted by an infrared LED.

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An infrared-sensitive transducer in the RECEIVER section detects the LED light pulses.

The RECEIVER circuitry converts the serial data back to parallel data and displays it on a group of four

LEDs to verify proper transmission.

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PROCEDURE

In this PROCEDURE, you will become familiar with the connections and operation of the circuit blocks

on your TRANSDUCER FUNDAMENTALS circuit board. You will verify your results by performing

calibrations and taking measurements.

Place a two-post connector in the OVEN ENABLE position of the IC TRANSDUCER circuit

block. Place a shunt in the 40 C position of the TEMP header. Complete the following steps

as you wait for the oven to reach 40 C.

Set your multimeter to measure volts dc. Connect the leads to OUT (+) and GND (–).

NOTE: All of the GND jacks on your circuit board are connected together. However, for best results,

always ground the meter or oscilloscope to the GND jack closest to where the measurement is taken.

The IC TRANSDUCER circuit block contains a current-to-voltage converter that translates

The circuit also scales the voltage to a value of 0.5 V for each degree of temperature change

C). An offset is used to set the output to 0 V at 30 C. The output voltage expressed as a

function of temperature (T) is therefore:

VO = (T - 30) x 0.5

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What output voltage would you expect at 40 C?

VO = V (Recall Value 1)

oven is up to temperature.

Measure VO.

VO = V (Recall Value 2)

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Is your measurement of V (Step 4, Recall Value 2) close to your calculated value

of V (Step 2, Recall Value 1)?

a. yes

b. no

Leave the two-post connector and TEMP shunt in place until you are instructed to remove

them.

Resistive-type transducers such as the thermistor and RTD are easily measured by using

resistance bridge circuits such as the Wheatstone bridge shown.

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The bridge output voltage is typically small and can be increased by a differential instrumentation

In the THERMISTOR circuit block, insert 2 two-post connectors as shown.

Set the multimeter to measure volts dc. Connect the (+) lead to +OUT and the (–) lead to

–OUT.

C, with a

0 V output at 30 C.

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The output at 40 C should be 50 mV. Adjust the CAL pot for a voltmeter reading of 50 mV.

The circuit is now calibrated and you should read the correct voltage at any oven setting. This is

a typical calibration procedure for a temperature measurement circuit.

Remove the two-post connectors and meter leads from the THERMISTOR circuit block.

Insert a two-post connector in the RTD circuit block as shown.

Connect the voltmeter leads to OUT (+) and GND (–).

The RTD circuit block does not have a Wheatstone bridge, but it uses another circuit to convert

C, with a 0 V output at 30 C.

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The output at 40 C should be 50 mV. Adjust the CAL pot for a 50 mV reading on the

voltmeter.

Move the TEMP shunt in the IC TRANSDUCER circuit block to 45 C. Complete the following

steps as you allow the oven to reach this temperature.

As with the THERMISTOR circuit block, you have calibrated the RTD circuit block at a 40 C

reference temperature. You should now read the correct output voltage at any oven temperature

setting.

Observe the OVEN ON LED and allow it to complete several cycles to make sure the oven

is at 45 C.

Measure the output voltage at 45 C.

VO = mV (Recall Value 3)

C, the output voltage

should be 75 mV. Is this close to your measured value of (Step 15,

Recall Value 3) mV?

a. yes

b. no

Remove the meter connections from the RTD circuit block. Connect a patch lead from the

OUT jack in the RTD circuit block to the +IN jack in the INSTRUMENTATION AMPLIFIER

circuit block.

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Connect a patch lead from –IN to GND in the INSTRUMENTATION AMPLIFIER circuit block.

You measured mV (Step 15, Recall Value 3) at the RTD circuit block

output. What voltage should you read at IA OUT?

IA OUT = V (Recall Value 4)

Connect the meter leads to IA OUT (+) and GND (–) in the INSTRUMENTATION AMPLIFIER

circuit block.

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IA OUT = V (Recall Value 5)

due to its high common-mode rejection ratio.

Remove all connections from the RTD and INSTRUMENTATION AMPLIFIER circuit blocks.

Return the TEMP shunt in the IC TRANSDUCER circuit block to the 40 C position. Complete

the following steps as you wait for the oven to reach the new temperature.

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Connect patch leads from +OUT and –OUT in the THERMOCOUPLE circuit block to –IN

and +IN (respectively) in the INSTRUMENTATION AMPLIFIER circuit block.

Connect the voltmeter leads to IA OUT (+) and GND (–) in the INSTRUMENTATION

AMPLIFIER circuit block.

You can see that the THERMOCOUPLE circuit block has two potentiometers. They are labeled

CAL (calibration) and REF (reference).

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The THERMOCOUPLE circuit block has a two-step calibration procedure that is different from

that of the other temperature transducers.

–204 mV.

switch.

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Move the (+) meter lead to AMP OUT in the THERMOCOUPLE circuit block.

Connect a patch lead from IA OUT in the INSTRUMENTATION AMPLIFIER circuit block to

AMP IN in the THERMOCOUPLE circuit block.

C with a 0 V output at 30 C.

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The output voltage at 40 C should be 5.0 V. Adjust the CAL pot for a reading of 5.0 V at AMP

OUT.

VI = –204 mV

VO = +5.0 V

a. scales it

b. inverts the polarity

c. Both of the above

NOTE: In the previous steps, you calibrated the temperature transducer circuits with and without the

reading at the output.

Remove all connections from the RTD, INSTRUMENTATION AMPLIFIER, and IC

TRANSDUCER circuit blocks.

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By manually turning the knob, you can rotate the screw clockwise or counterclockwise.

The rotation of the screw raises or lowers a block, which in turn forces the free end of the beam

upward or downward.

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amount of force that is applied to the free end of the beam.

A negative voltage indicates that the beam is bent upward

A positive voltage indicates that the beam is bent downward

a. compressive

b. tensile

c. both compressive and tensile

d. none

For accurate measurements, you must zero the output voltage

Insert a two-post connector in the STRAIN GAUGE circuit block as shown.

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Connect the voltmeter leads to AMP OUT (+) and GND (–).

Use the adjustment tool supplied with your TRANSDUCER FUNDAMENTALS circuit board

to rotate the ZERO potentiometer for a voltmeter reading of 0 ±50 mV.

NOTE: The ZERO adjustment is a multi-turn pot.

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You have adjusted the output voltage to zero with no load on the beam. This step is necessary

for accurate results over the entire measurement range.

Remove the two-post connector and the meter leads from the STRAIN GAUGE circuit block.

One of the functions of the capacitance sensor is to sense position.

The variable capacitor is combined with resistors and an IC to make up an RC oscillator whose

output indicates the position of the plate.

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Insert the BLOCK ENABLE two-post connector in the CAPACITANCE SENSOR circuit

block.

Connect the oscilloscope channel 1 probe to OUT and ground the probe to GND.

Adjust the scope controls to view a square wave output signal.

Remove the BLOCK ENABLE connection.

What happens to the waveform?

a. amplitude increases

b. frequency increases

c. signal disappears

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Remove all connections from the CAPACITANCE SENSOR circuit block.

The TRANSMITTER section of the INFRARED CONTROLLER circuit block contains an encoder

that converts the binary information on the DIP switches into pulses that are sent via the LED.

The RECEIVER section has a decoder that reads the pulses from the light sensor and converts

them into digital signals that are displayed on the DATA LEDs.

Insert a BLOCK ENABLE two-post connector in the INFRARED CONTROLLER circuit block.

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Connect the oscilloscope CH 1 probe to the DECODER IN jack in the RECEIVER section.

Ground the probe to the GND jack.

Set the DIP switch code to 0000 (all switches down).

Observe the oscilloscope as you press the XMT button several times.

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Set the DIP switch code to 1111 (all switches up) and repeat step 44.

What can you conclude from the waveforms?

a. Only code 1111 was received.

b. Only code 0000 was received.

c. Both codes were received.

Remove the two-post connector and scope connections from the INFRARED

CONTROLLER circuit block.

CONCLUSION

• The TRANSDUCER FUNDAMENTALS circuit board has eight transducer circuit blocks and three

auxiliary circuit blocks.

•

• The IC TRANSDUCER circuit block contains an oven controller that regulates oven temperature for

all four temperature transducer blocks.

• Some of the circuit blocks have calibration adjustment pots to establish an accurate relationship of

the input quantity to the output parameter.

• Circuit blocks that have a BLOCK ENABLE connection require a two-post connector in this position to

operate.

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REVIEW QUESTIONS

1. Which temperature transducer circuit block do you not need to calibrate for temperature

measurement?

a. IC TRANSDUCER

b. THERMISTOR

c. RTD

d. THERMOCOUPLE

2. Which auxiliary circuit block is used to increase the signal from the transducer circuit blocks?

a. OVEN

b. INSTRUMENTATION AMPLIFIER

c. REFERENCE SUPPLY

d. All of the above

3. Which transducer circuit block does not have BLOCK ENABLE jacks?

a. INFRARED CONTROLLER

b. CAPACITANCE SENSOR

c. STRAIN GAUGE

d. ULTRASONIC TRANSDUCERS

4. What can you use to connect the THERMISTOR circuit block to the INSTRUMENTATION AMPLIFIER

circuit block?

a. two-post connectors

b. patch leads

c. DIP switches

d. None of the above

5. How can you regulate the oven temperature?

a. by calibrating the THERMISTOR circuit block

b. by calibrating the RTD circuit block

c. by calibrating the THERMOCOUPLE circuit block

d. by using a shunt on the TEMP header in the IC TRANSDUCER circuit block

Documents

Exercise 2: Introduction to the Circuit Board Manual 28 FACET by Lab-Volt Familiarization Transducer Fundamentals Exercise 2: Introduction to the Circuit Board EXERCISE OBJECTIVE When