PASCO PS-2148 User Manual

Instruction Manual

IR Sensor

PS-2148

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No. 012-08852A

PS-2148

IR Sensor

Shutter
Thumbscrew
& Washer

Included Equipment Part Number

IR Sensor

Shutter with thumbscrew and washer

Sensor Handle

PS-2148

003-08860

CI-9874 (4-pack)

Additional Equipment Required

PASPORT interfa c e

DataStudio or DataStudio Lite

(required for computer-based data collection)

See PASCO catalog or www.pasco.com

See PASCO catalog or www.pasco.com
DS Lite available for free download

Additional Equipment Recommended

PASPORT Extension Cord

Aperture Bracket

PS-2500

OS-8534

Sensor Handle

Thermal Cavity

TD-8580

Introduction

The PASPORT IR Sensor measures infrared radiation intensity over a broad spectrum,
allowing students to study a variety of phenomena including blackbody radiation, the
Stefan-Boltzmann law, heat flow by radiation, solar radiance and non-contact temperature
measurement.

IR Sensor Sensor Setup

The sensor's silicon-based thermopile encapsulated in nitrogen with a
thallium bromide-iodide (KRS-5) window has a flat spectral response
from 0.7 to 30 µm. It measures radiation intensity up to 4500 W/m

2

. An
integrated thermistor measures the temperature of the detector allowing
the user to calculate detector-emitted radiation. In conjunction with a
PASPORT interface, the IR Sensor measures and records thermopile
voltage, radiation intensity and detector temperature at up to 100
samples per second.

Sensor Setup

Connect the IR sensor to a PASPORT interface either directly, or via a
PASPORT extension cord. If you are using a computer, connect the
interface to the USB port and start DataStudio.

By default the sampling rate of the sensor is 100 Hz. To change it, go to
the Experiment Setup window in DataStudio, or the Sensors screen of
the Xplorer GLX. To set up the sensor for estimating the temperature of
objects, see “Non-contact Temperature Sensor Simulation” on page 5.

If desired, connect the sensor handle to the ¼-20 threaded connector on
the sensor. This connector can also be used with any other ¼-20 screw.

It is not always necessary to attach the shutter, but it can be useful to
control the detector temperature. Install the shutter as shown using the
included thumbscrew and washer. Or use the sensor handle in place of
the thumbscrew.

To measure net IR intensity, point the sensor at a surface or object, such
as your hand or the sun, and start data collection in DataStudio or the
PASPORT interface. In DataStudio, intensity is automatically shown in
a digits display. In DataStudio or on the Xplorer GLX the data can also
be displayed in a graph, table, or meter.*

Background

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Sensor Handle

and Shutter
Attachment

*Refer to the DataStudio
Help menu, or the
Xplorer GLX Users’
Guide for information on
setting up data displays.

IR Radiation

All objects emit IR radiation.The radiated power per unit area of an
object is given by the Stefan-Boltzmann law:

I = εσT

4

Where T is the objects’ absolute surface temperature, and σ is the
Stefan-Boltzmann constant, equal to 5.670 × 10-8 W⋅m-2⋅K-4. The
emissivity, ε, is a property of the object’s surface and can range from 0
to 1. An object with ε = 1 is described as a blackbody.

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Model No. PS-2148 Background

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Theory of Operation

Consider a blackbody of temperature Ts, whose shape can be

T

s

Source

approximated as an infinite plane, and a flat detector surface parallel to
source with area Ad.

P

sd

Because radiation from an infinite plane propagates as a plane wave,
the power flow from the source to the detector (Psd) equals the radiation
emitted by a part of the source whose area is equal to the detector’s

P

d

area, regardless of the distance between the source and detector.

DT

Psd = AdσT

Thermopile

4

s

T

d

V

The detector itself also radiates in accordance to the Stefan-Boltzmann
law. If the detector’s temperature is Td, then power radiating out of the
detector is

Pd = AdσT

4

d

Therefore, the net power absorbed by the detector is

4

P = Adσ(T

The net intensity, which is what the sensor measures, is the net power

s

− T

4

)

d

divided by the detector area.

The net power that flows onto the active detector area by radiation
(Psd− Pd) flows out of the detector by conduction to other parts of the
sensor. A proportion of that power is conducted through the thermopile,
which sets up a temperature different (∆T) across the thermopile. The
thermopile produces a voltage (V) that is proportional to ∆T.

If the sensor is warmer than the target source, then net power flows out
of the sensor, and ∆T and V are negative.

The net radiated power (P) is proportional the power flow through the
thermopile, which is proportional to ∆T, which, in turn, is proportional

What is a thermopile?

A thermopile is a series
of thermocouples

A thermocouple is the

unction of two different
metals. When two
thermocouples are
connected in series, and
are at different
temperatures, a voltage
proportional to the
temperature difference
occurs between them.

This voltage is usually
very small. In a
thermopile many
thermocouples are
connected in series (as
shown below) to produce
a larger voltage. The
thermopile in the
PS-2148 consists of 120

unctions etched in
silicon.

Hot

to V; therefore, V is proportional to P:

D

T

V = R P

Cold

The constant, R, is known as the responsivity of the detector. For the
PS-2148 sensor, R is about 31 V/W.

The sensor amplifies the voltage produced by the thermopile and

V

Pair of

Thermocouples

converts it into a digital signal. A microprocessor in the sensor
calculates intensity, which is incident power divided by the area of the
detector (2.25 mm2). The thermopile voltage and intensity data are sent
digitally to the PASPORT interface or computer.

Hot

Cold

D

T

V

Thermopile

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