Measurement Computing USB-5200 Series User manual

USB-5203
Multi-sensor Measurement and Data Logger
Document Revision 14A
January 2015
©Copyright 2015
User's Guide

2
HM USB-5203
Trademark and Copyright Information
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Other product and company namesmentioned herein are trademarks or trade names of their respective
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©2015 MeasurementComputingCorporation. All rights reserved. No part of this publicationmay be
reproduced, stored in a retrieval system, or transmitted, in any form by any means, electronic,mechanical, by
photocopying, recording, or otherwise without the prior written permission of Measurement Computing
Corporation.
Notice
Measurement Computing Corporation does not authorize any Measurement Computing Corporation product for
use in life support systems and/or devices without prior written consent from Measurement Computing
Corporation. Life support devices/systems are devices or systems that, a) are intended for surgical implantation
into the body, or b) support or sustain life and whose failure to perform can be reasonably expected to result in
injury. Measurement Computing Corporation products are not designed with the components required, and are
not subject to the testing required to ensure a level of reliability suitable for the treatment and diagnosis of
people.

3
Table of Contents
Preface
About this User’s Guide.......................................................................................................................5
What you will learn from this user's guide .........................................................................................................5
Conventions in this user's guide .........................................................................................................................5
Where to find more information.........................................................................................................................5
Chapter 1
Introducing the USB-5203 ....................................................................................................................6
Logging data with the USB-5203 ..................................................................................................................................... 6
Functional block diagram...................................................................................................................................7
Chapter 2
Installing the USB-5203 ........................................................................................................................8
Unpacking...........................................................................................................................................................8
Installing the software ........................................................................................................................................8
Installing the hardware .......................................................................................................................................8
Firmware revision 2.12 and earlier ................................................................................................................................... 8
Firmware revision 3.0 and later ........................................................................................................................................ 8
Configuring the hardware...................................................................................................................................9
Configuring data logging options...................................................................................................................................... 9
Calibrating the hardware.....................................................................................................................................9
Factory calibration............................................................................................................................................................ 9
Field-calibration................................................................................................................................................................ 9
Chapter 3
Sensor Connections ...........................................................................................................................10
Screw terminal pin out......................................................................................................................................10
Sensor input terminals (C0H/C0L to C7H/C7L)..............................................................................................................10
Current excitation output terminals (±I1 to ±I4)..............................................................................................................11
Four-wire, two sensor common terminals (4W01 to 4W67)............................................................................................11
Two sensor common terminals (IC01 to IC67)................................................................................................................11
Digital terminals (DIO0 to DIO7)....................................................................................................................................11
CJC sensors......................................................................................................................................................................11
Power terminals (+5V).....................................................................................................................................................11
Ground terminals (GND).................................................................................................................................................11
Thermocouple connections...............................................................................................................................11
Wiring configuration........................................................................................................................................................12
RTD and thermistor connections......................................................................................................................12
Two-wire configuration ...................................................................................................................................................13
Three-wire configuration .................................................................................................................................................14
Four-wire configuration...................................................................................................................................................14
Semiconductor sensor measurements...............................................................................................................15
Wiring configuration........................................................................................................................................................15
Digital I/O connections.....................................................................................................................................16
Configuring the DIO channels to generate alarms ...........................................................................................................16
Chapter 4
Functional Details ...............................................................................................................................17
Thermocouple measurements...........................................................................................................................17
Cold junction compensation (CJC)..................................................................................................................................17
Data linearization.............................................................................................................................................................17
Open-thermocouple detection (OTD) ..............................................................................................................................17
RTD and thermistor measurements ..................................................................................................................18
Data linearization.............................................................................................................................................................18
External components ........................................................................................................................................18

USB-5203 User's Guide
4
Screw terminals................................................................................................................................................................18
USB connector.................................................................................................................................................................19
LED .................................................................................................................................................................................19
CompactFlash®memory card slot....................................................................................................................................19
Data logging button .........................................................................................................................................................20
External power supply......................................................................................................................................21
Disconnecting the USB-5203 from the computer.............................................................................................21
Transferring binary data after a logging session...............................................................................................21
Converting binary data after a logging session.................................................................................................21
Chapter 5
Specifications......................................................................................................................................22
Analog input .....................................................................................................................................................22
Channel configurations.....................................................................................................................................22
Compatible sensors...........................................................................................................................................23
Accuracy...........................................................................................................................................................23
Thermocouple measurement accuracy.............................................................................................................................23
Semiconductor sensor measurement accuracy.................................................................................................................24
RTD measurement accuracy............................................................................................................................................24
Thermistor measurement accuracy ..................................................................................................................................25
Throughput rate to PC ......................................................................................................................................25
Digital input/output...........................................................................................................................................26
Temperature alarms..........................................................................................................................................27
Memory ............................................................................................................................................................27
Microcontroller.................................................................................................................................................27
Data Logging....................................................................................................................................................28
Real time clock.................................................................................................................................................28
USB +5V voltage .............................................................................................................................................29
Power................................................................................................................................................................29
USB specifications ...........................................................................................................................................29
Current excitation outputs (Ix+) .......................................................................................................................30
Environmental ..................................................................................................................................................30
Mechanical .......................................................................................................................................................30
Screw terminal connector.................................................................................................................................30
Declaration of Conformity..................................................................................................................32

5
Preface
About this User’s Guide
What you will learn from this user's guide
This user's guide describes the Measurement Computing USB-5203 data acquisition device and lists device
specifications.
Conventions in this user's guide
For more information
Text presented in a box signifies additional information related to the subject matter.
Caution! Shaded caution statements present information to help you avoid injuring yourself and others,
damaging your hardware, or losing your data.
bold text Bold text is used for the names of objects on a screen, such as buttons, text boxes, and check boxes.
italic text Italic text is used for the names of manuals and help topic titles, and to emphasize a word or phrase.
Where to find more information
Additional information about USB-5203 hardware is available on our website at www.mccdaq.com. You can
also contact Measurement Computing Corporation with specific questions.
Knowledgebase: kb.mccdaq.com
Tech support form: www.mccdaq.com/support/support_form.aspx
Email: [e-mail]
Phone: [phone] and follow the instructions for reaching Tech Support
For international customers, contact your local distributor. Refer to the International Distributors section on our
website at www.mccdaq.com/International.

6
Chapter 1
Introducing the USB-5203
The USB-5203 provides eight differential input channels that are software-programmable for different sensor
categories including thermocouple, RTDs, thermistors, and semiconductor sensors.
Eight independent, TTL-compatible digital I/O channels are provided to monitor TTL-level inputs,
communicate with external devices, and to generate alarms. The digital I/O channels are software-
programmable for input or output.
With the USB-5203, you can take measurements from four sensor categories:
Thermocouple – types J, K, R, S, T, N, E, and B
Resistance temperature detectors (RTDs) – 2, 3, or 4-wire measurements of 100 Ω platinum RTDs
Thermistors – 2, 3, or 4-wire measurements
Semiconductor temperature sensors – LM36 or equivalent
The USB-5203 provides a 24-bit analog-to-digital (A/D) converter for each pair of differential analog input
channels. Each pair of differential inputs constitutes a channel pair.
You can connect a different category of sensor to each channel pair, but you cannot mix categories among the
channels that constitute a channel pair (although it is permissible to mix thermocouple types).
The USB-5203 provides two integrated cold junction compensation (CJC) sensors for thermocouple
measurements, and built-in current excitation sources for resistive sensor measurements.
An open thermocouple detection feature lets you detect a broken thermocouple. An on-board microprocessor
automatically linearizes the measurement data according to the sensor category.
The USB-5203 features eight independent temperature alarms. Each alarm controls an associated digital I/O
channel as an alarm output. The input to each alarm is one of the temperature input channels. The output of each
alarm is software configurable as active high or low. You set up the temperature threshold conditions to activate
each alarm. When an alarm is activated, the associated DIO channel is driven to the output state.
You can log your sensor measurements to a CompactFlash®memory card. CompactFlash is a removable non-
volatile storage device. A 512 MB CompactFlash memory card is shipped with the device to store your data.
For more information, refer to Logging data with the USB-5203 below.
The USB-5203 device is compatible with both USB 1.1 and USB 2.0 ports. The speed of the device may be
limited when using a USB 1.1 port due to the difference in transfer rates on the USB 1.1 versions of the
protocol (low-speed and full-speed).
External power is required for data logging operations
Due to processing limitations, you cannot log data to the memory card when the USB-5203 is connected to your
computer's active USB bus. When operating as a data logger, disconnect the USB cable from the computer, and
connect the external power supply shipped with the device.
The USB-5203 is a standalone plug-and-play device. External power is required for data logging mode only. All
configurable options are software programmable. The USB-5203 is fully software calibrated.
Logging data with the USB-5203
Due to processing limitations, you cannot log data to the memory card when the USB-5203 is connected to an
active USB port. When operating as a data logger, disconnect the USB cable from the computer, and connect
the external power supply shipped with the device.
The USB-5203 has many software-selectable options for setting up data logging.
You can record:
temperature (°C) or raw data from selected input channels
timestamp data
CJC sensor readings

USB-5203 User's Guide Introducing the USB-5203
7
You can specify the number of seconds between samples. You can begin logging data at power up, when you
press the data logging button, or at a specific date and time.
Data is stored on the memory card in binary files. After logging measurements, you can transfer the files to your
computer. You can use InstaCal to convert the files to .csv format for use in Microsoft Excel files, or to .txt
format for use in other applications.
Functional block diagram
USB-5203 functions are illustrated in the block diagram shown here.
Figure 1. Functional block diagram

8
Chapter 2
Installing the USB-5203
Unpacking
As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the device from its packaging, ground yourself using a wrist strap or by simply
touching the computer chassis or other grounded object to eliminate any stored static charge.
Contact us immediately if any components are missing or damaged.
Installing the software
Refer to the MCC DAQ Quick Start for instructions on installing the software on the MCC DAQ CD. Refer to
the device product page on the Measurement Computing website for information about the included and
optional software supported by the USB-5203.
Install the software before you install your device
The driver needed to run the USB-5203 is installed with the software. Therefore, you need to install the
software package you plan to use before you install the hardware.
Installing the hardware
To connect the USB-5203 to your system, turn your computer on, and connect the USB cable to a USB port on
your computer or to an external USB hub that is connected to your computer. The USB cable provides power
and communication to the USB-5203.
If you are connecting the USB-5203 to an external self-powered hub, connect the USB hub to the computer
before you connect the device to the hub. This ensures that the device detects the hub as an active USB port.
Firmware revision 2.12 and earlier
When you connect the USB-5203 for the first time, a Found New Hardware dialog opens when the operating
system detects the device. When the dialog closes, the installation is complete. The device LED will blink and
then remain on. This indicates that communication is established between the USB-5203 and your computer.
Firmware revision 3.0 and later
The USB-5203 installs as a composite device with separate devices attached. When you connect the USB-5203
for the first time, a Found New Hardware dialog opens as each USB-5203 interface is detected.
It is normal for multiple dialogs to open when you connect the USB-5203 for the first time. For additional
information, refer to the "Notes on installing and using the USB-5201 and USB-5203 data logging devices" that
ships with the device.
When the last dialog closes the installation is complete. The LED on the USB-5203 will blink and then remain
on. This indicates that communication is established between the USB-5203 and your computer.
Caution! Do not disconnect any device from the USB bus while the computer is communicating with the
USB-5203, or you may lose data and/or your ability to communicate with the USB-5203.
If the LED turns off
If the LED is lit but then turns off, the computer has lost communication with the USB-5203. To restore
communication, disconnect the USB cable from the computer, and then reconnect it. This should restore
communication, and the LED should turn back on.

USB-5203 User's Guide Installing the USB-5203
9
Configuring the hardware
All hardware configuration options on the USB-5203 are software-selectable. The configurable options
dynamically update according to the selected sensor category. All hardware configuration options on the USB-
5203 are software-selectable. Settings are stored on an isolated microcontroller in EEPROM – which is non-
volatile memory on the USB-5203 – and are loaded on power-up.
Default configuration
The factory default sensor type configuration is Disabled. The disabled mode disconnects the analog inputs
from the terminal blocks and internally grounds all of the A/D inputs. This mode also disables each of the
current excitation sources.
Warm up
Allow the USB-5203 to warm up for 30 minutes before taking measurements. This warm up time minimizes
thermal drift and achieves the specified rated accuracy of measurements. For RTD or thermistor measurements,
this warm-up time is also required to stabilize the internal current reference.
Configuring data logging options
The following data logging options are programmable with software.
select the input channels to log
set the data format
set the start mode
set up alarm conditions
copy and convert saved binary files
delete data files
All data logging options are stored on the USB-5203 in non-volatile memory in EEPROM, and are loaded on
power up.
Calibrating the hardware
Factory calibration
The Measurement Computing Manufacturing Test department performs the initial factory calibration. Return
the device to Measurement Computing Corporation when calibration is required. The recommended calibration
interval is one year.
Field-calibration
The USB-5203 supports field-calibration with InstaCal. Calibrate the device whenever the ambient temperature
changes by more than ±10 °C from the last self-calibration.
Allow the USB-5203 to operate for at least 30 minutes before calibrating.

10
Chapter 3
Sensor Connections
The USB-5203 supports the following temperature sensor types:
Thermocouple – types J, K, R, S, T, N, E, and B
Resistance temperature detectors (RTDs) – 2, 3, or 4-wire measurement modes of 100 Ω platinum RTDs.
Thermistors – 2, 3, or 4-wire measurement modes.
Semiconductor temperature sensors – LM36 or equivalent
Sensor selection
The type of sensor you select will depend on your application needs. Review the temperature ranges and
accuracies of each sensor type to determine which is best suited for your application.
Screw terminal pin out
The USB-5203 has four rows of screw terminals – two rows on the top edge of the housing, and two rows on
the bottom edge. Each row has 26 connections. Between each bank of screw terminals are two integrated CJC
sensors used for thermocouple measurements. Signals are identified in Figure 2.
Figure 2. USB-5203 screw terminal pin numbers
Use 16 AWG to 30 AWG wire for your signal connections.
Tighten screw terminal connections
When making connections to the screw terminals, fully tighten the screw. Simply touching the top of the screw
terminal is not sufficient to make a proper connection.
Sensor input terminals (C0H/C0L to C7H/C7L)
You can connect up to eight temperature sensors to the differential sensor inputs (C0H/C0L to C7H/C7L).
Supported sensor categories include thermocouples, RTDs, thermistors, or semiconductor sensors.
Do not mix sensor categories within channel pairs. It is permitted to mix thermocouple types (J, K, R, S, T, N,
E, and B) within channel pairs, however.

USB-5203 User's Guide Sensor Connections
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Do not connect two different sensor categories to the same channel pair
The USB-5203 provides a 24 bit A/D converter for each channel pair. Each channel pair can monitor one sensor
category. To monitor a sensor from a different category, connect the sensor to a different channel pair (input
terminals).
Current excitation output terminals (±I1 to ±I4)
The USB-5203 has four dedicated pairs of current excitation output terminals (±I1 to ±I4). These terminals have
a built-in precision current source to provide excitation for the resistive sensors used for RTD and thermistor
measurements.
Each current excitation terminal is dedicated to one pair of sensor input channels:
I1+ is the current excitation source for channel 0 and channel 1
I2+ is the current excitation source for channel 2 and channel 3
I3+ is the current excitation source for channel 4 and channel 5
I4+ is the current excitation source for channel 6 and channel 7
Four-wire, two sensor common terminals (4W01 to 4W67)
These terminals are used as the common connection for four-wire configurations with two RTD or thermistor
sensors.
Two sensor common terminals (IC01 to IC67)
These terminals are used as the common connection for two-wire configurations with two RTD or thermistor
sensors.
Digital terminals (DIO0 to DIO7)
You can connect up to eight digital I/O lines to the screw terminals labeled DIO0 to DIO7. Each terminal is
software-configurable for input or output.
If a digital bit is set up as an alarm, the bit is configured for output on power-up, and assumes the state defined
by the alarm configuration.
CJC sensors
The USB-5203 has two built in high-resolution temperature sensors. One sensor is located on the right side of
the package, and one sensor is located on the left side.
Power terminals (+5V)
The two +5V output terminals are isolated (500 VDC) from the USB +5V.
Caution! Each +5V terminal is an output. Do not connect to an external power supply to these terminals or
you may damage the USB-5203 and possibly the computer.
Ground terminals (GND)
The six ground terminals (GND) provide a common ground for the input channels and DIO bits and are isolated
(500 VDC) from the USB GND.
Thermocouple connections
The USB-5203 makes fully-differential thermocouple measurements without the need of ground-referencing
resistors. A 32-bit floating point value in either a voltage or temperature format is returned by software. An
open thermocouple detection feature is available for each analog input which automatically detects an open or
broken thermocouple.
Use InstaCal to select the thermocouple type (J, K, R, S, T, N, E, and B) and one or more sensor input channels
to connect the thermocouple.

USB-5203 User's Guide Sensor Connections
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Wiring configuration
Connect the thermocouple to the USB-5203 using a differential configuration, as shown in Figure 3.
Figure 3. Typical thermocouple connection
The USB-5203 GND pins are isolated from earth ground, so connecting thermocouple sensors to voltages
referenced to earth ground is permissible as long as the isolation between the GND pins (9, 19, 28, 38) and earth
ground is maintained.
When thermocouples are attached to conductive surfaces, the voltage differential between multiple
thermocouples must remain within ±1.4 V. For best results, we recommend the use of insulated or ungrounded
thermocouples when possible.
Maximum input voltage between analog input and ground
The absolute maximum input voltage between an analog input and the isolated GND pins is ±25 VDC when the
USB-5203 is powered on, and ±40 VDC when the USB-5203 is powered off.
If you need to increase the length of your thermocouple, use the same type of thermocouple wires to minimize
the error introduced by thermal EMFs.
RTD and thermistor connections
A resistance temperature detector (RTD) measures temperature by correlating the resistance of the RTD
element with temperature. A thermistor is a thermally-sensitive resistor that is similar to an RTD in that its
resistance changes with temperature – thermistors show a large change in resistance that is proportional to a
small change in temperature. The main difference between RTD and thermistor measurements is the method
used to linearize the sensor data.
RTDs and thermistors are resistive devices that require an excitation current to produce a voltage drop that can
be measured differentially across the sensor. The device has four built-in current excitation sources (±I1 to ±I4)
for measuring resistive type sensors. Each current excitation terminal is dedicated to one channel pair.
The USB-5203 makes two, three, and four-wire measurements of RTDs (100 Ω platinum type) and thermistors.
Use InstaCal to select the sensor type and the wiring configuration. Once the resistance value is calculated, the
value is linearized in order to convert it to a temperature value. A 32-bit floating point value in either
temperature or resistance is returned by software.
RTD maximum resistance
Resistance values greater than 660 Ω cannot be measured in RTD mode. The 660 Ω resistance limit includes the
total resistance across the current excitation (±Ix) pins, which is the sum of the RTD resistance and the lead
resistances.
Thermistor maximum resistance
Resistance values greater than 180 kΩ cannot be measured in thermistor mode. The 180 kΩ resistance limit
includes the total resistance across the current excitation (±Ix) pins, which is the sum of the thermistor
resistance and the lead resistance.

USB-5203 User's Guide Sensor Connections
13
Two-wire configuration
The easiest way to connect an RTD sensor or thermistor to the USB-5203 is with a two-wire configuration,
since it requires the fewest connections to the sensor. With this method, the two wires that provide the RTD
sensor with its excitation current also measure the voltage across the sensor.
Since RTDs exhibit a low nominal resistance, measurement accuracy can be affected due to the lead wire
resistance. For example, connecting lead wires that have a resistance of 1 Ω (0.5 Ω each lead) to a 100 Ω
platinum RTD will result in a 1% measurement error.
With a two-wire configuration, you can connect either one sensor per channel pair, or two sensors per channel
pair.
Two-wire, single-sensor
A two-wire single-sensor measurement configuration is shown in Figure 4.
Figure 4. Two-wire, single RTD or thermistor sensor measurement configuration
When you select a two-wire single sensor configuration with InstaCal, connections to C#H and C#L are made
internally.
Two-wire, two sensor
A two-wire, two-sensor measurement configuration is shown in Figure 5.
Figure 5. Two-wire, two RTD or thermistor sensors measurement configuration
When you select a two-wire, two sensor configuration with InstaCal, connections to C#H (first sensor) and
C#H/C#L (second sensor) are made internally.
When configured for two-wire mode, both sensors must be connected to obtain proper measurements.

USB-5203 User's Guide Sensor Connections
14
Three-wire configuration
A three-wire configuration compensates for lead-wire resistance by using a single-voltage sense connection.
With a three-wire configuration, you can connect only one sensor per channel pair. A three-wire measurement
configuration is shown in Figure 6.
Figure 6. Three-wire RTD or thermistor sensor measurement configuration
When you select a three-wire sensor configuration with InstaCal, the USB-5203 measures the lead resistance on
the first channel (C#H/C#L) and measures the sensor itself using the second channel (C#H/C#L). This
configuration compensates for any lead-wire resistance and temperature change in lead-wire resistance.
Connections to C#H for the first channel and C#H/C#L of the second channel are made internally.
Three-wire compensation
For accurate three wire compensation, the individual lead resistances connected to the ±I# pins must be of equal
resistance value.
Four-wire configuration
With a four-wire configuration, connect two sets of sense/excitation wires at each end of the RTD or thermistor
sensor. This configuration completely compensates for any lead-wire resistance and temperature change in lead-
wire resistance.
Connect your sensor with a four-wire configuration when your application requires very high accuracy
measurements. Examples of a four-wire single-sensor measurement configuration are shown in Figure 7 and
Figure 8.
You can configure the USB-5203 with either a single-sensor-per-channel, or a two-sensor–per-channel pair.
Four-wire, single-sensor
A four-wire, single-sensor connected to the first channel of a channel pair is shown in Figure 7.
Figure 7. Four-wire, single RTD or thermistor sensor measurement configuration
A four-wire, single-sensor connected to the second channel of a channel pair is shown in Figure 8.

USB-5203 User's Guide Sensor Connections
15
Figure 8. Four-wire, single RTD or thermistor sensor measurement configuration
A four-wire, two-sensor measurement configuration is shown in Figure 9.
Figure 9. Four-wire, two RTD or thermistor sensors measurement configuration
When configured for two-wire mode, both sensors must be connected to obtain proper measurements.
Semiconductor sensor measurements
Semiconductor sensors are suitable over a range of approximately -40 °C to 125 °C, where an accuracy of
±2 °C is adequate. The temperature measurement range of a semiconductor sensor is small when compared to
thermocouples and RTDs. However, semiconductor sensors can be accurate, inexpensive and easy to interface
with other electronics for display and control.
The USB-5203 makes high-resolution measurements of semiconductor sensors. The software outputs the
measurement data as a 32-bit floating point value in either voltage or temperature.
Use InstaCal to select the sensor type (LM35, TMP35 or equivalent) and the sensor input channel to connect the
sensor.
Wiring configuration
Connect the semiconductor sensor to the USB-5203 using a single-ended configuration, as shown in Figure 10.
The device provides +5V and GND pins for powering the sensor.
Figure 10. Semiconductor sensor measurement configuration

USB-5203 User's Guide Sensor Connections
16
Digital I/O connections
You can connect up to eight digital I/O lines to the screw terminals labeled DIO0 to DIO7. All digital I/O lines
are pulled up to +5V with a 47 kΩ resistor (default). You can request the factory to configure the resistor for
pull-down to ground if desired. You can configure each digital bit for either input or output.
Caution! If a digital bit is set up as an alarm, the bit will be configured for output on power-up, and assume
the state defined by the alarm configuration.
When you configure the digital bits for input, you can use the USB-5203 digital I/O terminals to detect the state
of any TTL-level input. Refer to the schematic shown in Figure 11. If you set the switch to the +5V input, DIO0
reads TRUE (1). If you move the switch to GND, DIO0 reads FALSE (0).
Figure 11. Schematic showing switch detection by digital channel DIO0
Caution! All ground pins on the USB-5203 (pins 9, 19, 28, 38) are common and are isolated from earth
ground. If a connection is made to earth ground when using digital I/O and conductive
thermocouples, the thermocouples are no longer isolated. In this case, thermocouples must not be
connected to any conductive surfaces that may be referenced to earth ground.
For general information regarding digital signal connections and digital I/O techniques, refer to the Guide to
Signal Connections (available on our web site at www.mccdaq.com/signals/signals.pdf).
Configuring the DIO channels to generate alarms
The USB-5203 features eight independent temperature alarms. All alarm options are software configurable.
When a digital bit is configured as an alarm, that bit will be configured as an output on the next power cycle and
assume the state defined by the alarm configuration.
Each alarm controls an associated digital I/O channel as an alarm output. The input to each alarm is one of the
temperature input channels. You set up the temperature conditions to activate an alarm, and the output state of
the channel (active high or low) when activated. When an alarm is activated, its associated DIO channel is
driven to the output state specified.
The alarm configurations are stored in non-volatile memory and are loaded on power up. The temperature
alarms function both in data logging mode and while attached to the USB port on a computer.

17
Chapter 4
Functional Details
Thermocouple measurements
A thermocouple consists of two dissimilar metals that are joined together at one end. When the junction of the
metals is heated or cooled, a voltage is produced that correlates to temperature.
The USB-5203 hardware level-shifts the thermocouple’s output voltage into the A/D’s common mode input
range by applying +2.5 V to the thermocouple’s low side at the C#L input. Always connect thermocouple
sensors to the USB-5203 in a floating fashion. Do not attempt to connect the thermocouple low side C#L to
GND or to a ground referencing resistor.
Cold junction compensation (CJC)
When you connect the thermocouple sensor leads to the sensor input channel, the dissimilar metals at the USB-
5203 terminal blocks produce an additional thermocouple junction. This junction creates a small voltage error
term which must be removed from the overall sensor measurement using a cold junction compensation
technique. The measured voltage includes both the thermocouple voltage and the cold junction voltage. To
compensate for the additional cold junction voltage, the USB-5203 subtracts the cold junction voltage from the
thermocouple voltage.
The USB-5203 has two high-resolution temperature sensors that are integrated into the design of the USB-5203.
One sensor is located on the right side of the package, and one sensor is located at the left side. The CJC sensors
measure the average temperature at the terminal blocks so that the cold junction voltage can be calculated. A
software algorithm automatically corrects for the additional thermocouples created at the terminal blocks by
subtracting the calculated cold junction voltage from the analog input's thermocouple voltage measurement.
Increasing the thermocouple length
If you need to increase the length of your thermocouple, use the same type of thermocouple wires to minimize
the error introduced by thermal EMFs.
Data linearization
After the CJC correction is performed on the measurement data, an on-board microcontroller automatically
linearizes the thermocouple measurement data using National Institute of Standards and Technology (NIST)
linearization coefficients for the selected thermocouple type.
The measurement data is then output as a 32-bit floating point value in the configured format (voltage or
temperature).
Open-thermocouple detection (OTD)
The USB-5203 is equipped with an open-thermocouple detection for each analog input channel. With OTD, any
open-circuit or short-circuit condition at the thermocouple sensor is detected by the software. An open channel
is detected by driving the input voltage to a negative value outside the range of any thermocouple output. The
software recognizes this as an invalid reading and flags the appropriate channel. The software continues to
sample all channels when OTD is detected.
Input leakage current
With open-thermocouple detection enabled, 105 nA (max.) of input leakage current is injected into the
thermocouple. This current can cause an error voltage to develop across the lead resistance of the thermocouple
that is indistinguishable from the thermocouple voltage you are measuring. You can estimate this error voltage
with the following formula:
error voltage = resistance of the thermocouple x 105 nA
To reduce the error, reduce the length of the thermocouple to lower its resistance, or lower the AWG of the wire
by using a wire with a larger diameter. With open-thermocouple detection disabled, 30 nA (max) of input
leakage current is injected into the thermocouple.

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RTD and thermistor measurements
RTDs and thermistors are resistive devices that require an excitation current to produce a voltage drop that can
be measured differentially across the sensor. The USB-5203 measures the sensor resistance by forcing a known
excitation current through the sensor and then measuring (differentially) the voltage across the sensor to
determine its resistance.
After the voltage measurement is made, the resistance of the RTD is calculated using Ohms law – the sensor
resistance is calculated by dividing the measured voltage by the current excitation level (±Ix) source. The value
of the ±Ix source is stored in local memory.
Once the resistance value is calculated, the value is linearized in order to convert it to a temperature value. The
measurement is returned by software as a 32-bit floating point value in a voltage, resistance or temperature
format.
Data linearization
An on-board microcontroller automatically performs linearization on RTD and thermistor measurements.
RTD measurements are linearized using a Callendar-Van Dusen coefficients algorithm (you select DIN,
SAMA, or ITS-90).
Thermistor measurements are linearized using a Steinhart-Hart linearization algorithm (you supply the
coefficients from the sensor manufacturer's data sheet).
External components
The USB-5203 has the following external components, as shown in Figure 12.
1 Screw terminal pins 1 to 26 4 Data logging button
2 Screw terminal pins 27 to 52 5 CompactFlash
®
memory card slot (with card)
3 LED 6 USB connector
Figure 12. External component locations
Screw terminals
Use the screw terminals for connecting temperature sensors and digital I/O lines. These terminals also provide
ground and power output connections. Refer to the "Sensor Connections" chapter for screw terminal
descriptions.

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USB connector
When not logging data, connect the USB cable to a USB port on your computer or to an external USB hub that
is connected to your computer. When connected to an active USB bus, the USB connector provides +5 V power
and communication. The voltage supplied through the USB connector is system-dependent, and may be less
than 5 V. No external power supply is required.
Due to processing limitations, you cannot log data when the device is attached to an active USB bus. For data
logging operations, connect the USB connector to the external power supply.
LED
The LED uses up to 5 mA of current. The function of the LED varies according to whether the USB-5203 is
connected to an active USB port, or when the device is logging data and connected to the external power
supply.
Refer to the table below for the function of the USB-5203 LED when the device is connected to an active USB
port and not logging data.
LED function when the USB-5203 is connected to an active USB port
LED Illumination Indication
Steady green The USB-5203 is connected to a computer or external USB hub.
Blinks continuously Data is being transferred.
Upon connection, the LED should flash a few times and then remain lit (indicates a successful
installation).
Blinks several times Initial communication is established between the USB-5203 and the computer.
Off The USB-5203 is not connected to an active USB port.
Refer to the table below for the function of the USB-5203 LED when the device is connected to the external
supply and is logging data. The function of the LED varies according to the selected logging mode.
LED function when the USB-5203 is logging data
Logging mode LED Illumination Indication
Logging off The LED is off. The USB-5203 is not logging data, and/or
the device is not powered
Start Logging on Power
Up The LED turns on when external power is connected, then blinks each time data is captured. Blinks when logging data.
Start Logging on Button The LED stays off until the data logging button is
pressed and held for approximately 1 second. At
that time, the LED turns on and blinks each time
data is captured.
Blinks when logging data.
Start Logging at
Specified Time The LED is off – blinks on once per second until the specified date/time to start logging is reached.
At that time, the LED turns on – blinks off each
time data is captured.
Blinks on once per second until specified
data/time to log data occurs. Then it turns
on and blinks each time data is captured.
Any logging mode Blinks rapidly (250 ms period) and continuously. The memory card is full.
The memory card was removed during
logging. Insert the memory card again
to stop the device blinking.
CompactFlash®memory card slot
The CompactFlash slot accepts standard memory cards. A 512 MB memory card is shipped with the device. For
extensive data logging, you can insert a higher capacity card of up to 2 GB. You must format the memory card
before logging data for the first time.

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Calculating the logging time for a memory card
Use the following formula to calculate the approximate amount of logging time in seconds that one of the
supported memory card allows. The USB-5203 supports 512 MB , 1 GB, and 2 GB CompactFlash memory
cards.
where

time = total disk time in seconds
NDisk = size of memory card in bytes
NDIO = 1 byte for digital I/O
nChannels = number of channels logged

R = logging rate in seconds
NTS = 6 bytes for timestamp, if enabled
NTemp = 4 bytes for a temperature reading
NCJC = 8 bytes if CJC sensor readings are
enabled
The following table provides examples of logging one channel and eight channels of temperature readings at the
max logging rate of 1 S/s to a 512 MB memory card with DIO, timestamp, and CJC sensor logging enabled:
Memory card
(bytes) DIO enabled Number of
channels Logging rate (S/s) Timestamp enabled Temperature reading CJC enabled
512,000,000 1 1 1 6 4 8
512,000,000 1 8 1 6 4 8
Data logging button
Use the data logging button to end a data logging session. The data logging button is also used to start recording
data when the logging mode is set in InstaCal to Start Logging on Button.
To begin recording data, press and hold the button until the LED begins to blink. The first sample is taken
one second after the LED illuminates.
When you first power on the USB-5203, wait at least five seconds before pressing the data logging button.
To achieve rated accuracy, allow the USB-5203 to warm up for 30 minutes before logging data.
To stop recording data, press and hold the button again until the LED is off.
Caution! To prevent loss of data, always use the button to stop logging. Make sure the data is written to the
memory card before you disconnect the device from the power source.
The device caches log data in volatile memory prior to writing to the memory card.
Pressing the data logging button has no effect when the USB-5203 is connected to an active USB port and not
logging data.
External power required for data logging
Due to processing limitations, data logging is not allowed when the USB-5203 is attached to an active USB bus.
The USB-5203 must be connected to the standalone power supply to perform data logging.