Measurement Computing USB-1616HS User manual

USB-1616HS
High-Speed Analog Input and Digital I/O
Document Revision 3A
December 2012
© Copyright 2012
User's Guide

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HM USB-1616HS-docmap.docx
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Notice
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people.

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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-1616HS...............................................................................................................6
Overview: USB-1616HS features.......................................................................................................................6
Chapter 2
Installing the USB-1616HS...................................................................................................................7
What comes with your USB-1616HS shipment?................................................................................................7
Hardware .......................................................................................................................................................................... 7
Optional components..........................................................................................................................................8
AI-EXP48......................................................................................................................................................................... 8
Additional documentation................................................................................................................................................. 8
Unpacking the USB-1616HS..............................................................................................................................8
Installing the software ........................................................................................................................................9
Installing the hardware .......................................................................................................................................9
Configuring the hardware.................................................................................................................................10
Connecting the board for I/O operations ..........................................................................................................10
Connectors, cables –main I/O connector.........................................................................................................................10
Screw terminal pin outs ...................................................................................................................................................11
DSUB25F expansion connector.......................................................................................................................................12
Cabling.............................................................................................................................................................................13
Chapter 3
Functional Details ...............................................................................................................................14
USB-1616HS components................................................................................................................................14
External power connector ................................................................................................................................................15
USB-1616HS block diagram............................................................................................................................16
Synchronous I/O –mixing analog, digital, and counter scanning ....................................................................16
Analog input.....................................................................................................................................................16
Analog input scanning .....................................................................................................................................................17
Thermocouple input..........................................................................................................................................19
Tips for making accurate temperature measurements......................................................................................................19
Digital I/O.........................................................................................................................................................20
Digital input scanning......................................................................................................................................................20
Digital outputs and pattern generation .............................................................................................................................20
Triggering.........................................................................................................................................................20
Hardware analog triggering .............................................................................................................................................21
Digital triggering..............................................................................................................................................................21
Software-based triggering................................................................................................................................................21
Stop trigger modes...........................................................................................................................................................22
Pre-triggering and post-triggering modes ........................................................................................................................22
Counter inputs ..................................................................................................................................................22
Tips for making high-speed counter measurements (> 1 MHz).......................................................................................22
Mapped channels .............................................................................................................................................................23
Counter modes.................................................................................................................................................................23
Debounce modes..............................................................................................................................................................24
Encoder mode..................................................................................................................................................................27

USB-1616HS User's Guide
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Timer outputs....................................................................................................................................................30
Example: Timer outputs...................................................................................................................................................30
Using multiple USB-1616HSs per PC..............................................................................................................30
Using detection setpoints for output control.....................................................................................................30
What are detection setpoints? ..........................................................................................................................................30
Setpoint configuration overview......................................................................................................................................31
Setpoint configuration......................................................................................................................................................32
Using the setpoint status register......................................................................................................................................33
Examples of control outputs ............................................................................................................................................34
Detection setpoint details.................................................................................................................................................36
FIRSTPORTC or timer update latency............................................................................................................................36
Chapter 4
Calibrating the USB-1616HS..............................................................................................................38
Chapter 5
Specifications......................................................................................................................................39
Analog input.....................................................................................................................................................39
Accuracy..........................................................................................................................................................................39
Thermocouples ................................................................................................................................................................40
Digital input/output...........................................................................................................................................40
Counters............................................................................................................................................................41
Input sequencer.................................................................................................................................................41
Triggering.........................................................................................................................................................42
Frequency/pulse generators ..............................................................................................................................42
Power consumption ..........................................................................................................................................42
External power..................................................................................................................................................43
USB specifications ...........................................................................................................................................43
Environmental ..................................................................................................................................................43
Mechanical .......................................................................................................................................................43
Signal I/O connectors and pin out.....................................................................................................................43
Declaration of Conformity..................................................................................................................46

5
Preface
About this User's Guide
What you will learn from this user's guide
This user's guide explains how to install, configure, and use the USB-1616HS so that you get the most out of its
analog input, digital I/O, and counter/timer I/O features.
This user's guide also refers you to related documents available on our web site and to technical support
resources.
Conventions in this user's guide
For more information
Text presented in a box signifies additional information and helpful hints related to the subject matter you are
reading.
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 the 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
For additional information relevant to the operation of your hardware, refer to the Documents subdirectory
where you installed the MCC DAQ software (C:\Program Files\Measurement Computing\DAQ by default), or
search for your device on our website at www.mccdaq.com.

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Chapter 1
Introducing the USB-1616HS
Overview: USB-1616HS features
The USB-1616HS is supported under popular Microsoft®Windows®operating systems. The USB-1616HS
board is a multifunction measurement and control board designed for the USB bus.
The USB-1616HS provides either eight differential or 16 single-ended analog inputs with 16-bit resolution. It
offers seven software-selectable analog input ranges of ±10 V, ±5 V, ±2 V, ±1 V, ±0.5 V, ±0.2 V, and ±0.1V.
You can configure up to eight of the analog inputs as differential thermocouple (TC) inputs.
The board has 24 high-speed lines of digital I/O, two timer outputs, and four 32-bit counters. It provides up to
4 MHz scanning on all digital input lines1.
Six banks of removable screw-terminal blocks provide connectivity to the analog input channels, digital I/O
lines, and counter/timer channels.
You can operate all analog input, digital I/O, and counter/timer I/O synchronously.
1Higher rates—up to 12 MHz—are possible depending on the platform and the amount of data being transferred.

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Chapter 2
Installing the USB-1616HS
What comes with your USB-1616HS shipment?
As you unpack your USB-1616HS, verify that the following components are included.
Hardware
USB-1616HS
USB cable (2-meter length)
TR-2U power supply and CA-1* line cord
AC-to-DC conversion power supply and cord plugs into the external power connector of the USB-1616HS.
* European customers: Contact Measurement Computing to order the CA-261 line cord for your region.

USB-1616HS User's Guide Installing the USB-1616HS
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Optional components
Expansion devices and cables that are compatible with the USB-1616HS must be ordered separately.
If you ordered any of the following products with your device, they should be included with your shipment.
AI-EXP48
Analog input expansion module adds up to 24 differential or 48 single-ended inputs to the USB-1616HS.
CA-96A expansion cable
Expansion cable for connecting to the AI-EXP48 expansion board.
Additional documentation
In addition to this hardware user's guide, you should also receive the Quick Start Guide (available in PDF at
www.mccdaq.com/PDFmanuals/DAQ-Software-Quick-Start.pdf). This booklet supplies a brief description of
the software you received with your USB-1616HS and information regarding installation of that software.
Please read this booklet completely before installing any software or hardware.
Unpacking the USB-1616HS
As with any electronic device, you should take care while handling to avoid damage from static
electricity. Before removing the USB-1616HS 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.
If any components are missing or damaged, notify Measurement Computing Corporation immediately by
phone, fax, or e-mail:
Phone: [phone] and follow the instructions for reaching Tech Support
Fax: [phone] to the attention of Tech Support
Email: [e-mail]

USB-1616HS User's Guide Installing the USB-1616HS
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Installing the software
Refer to the Quick Start Guide for instructions on installing the software on the Measurement Computing Data
Acquisition Software CD. This booklet is available in PDF at www.mccdaq.com/PDFmanuals/DAQ-Software-
Quick-Start.pdf.
We recommend that you download the latest Windows Update onto your computer before installing and
operating the USB-1616HS.
Installing the hardware
To connect the USB-1616HS to your system, turn your computer on, and then do the following:
Connect signal lines to the USB-1616HS's removable screw terminal blocks.
oConnect voltage signals as single-ended or differential connections (see Figure 1).
oConnect thermocouple signals as differential connections (see Figure 1). The negative (typically, the
red) thermocouple wire connects to the channel's LO connector, and the other color wire connects to
the channel's HI connector.
Always use differential input mode for thermocouple connections.
Figure 1. Single-ended voltage connections (V1and V2) and differential thermocouple connections (V3)
If you are using an AI-EXP48 expansion device, connect it to the USB-1616HS. Make sure you do not
connect the AI-EXP48 to a live USB-1616HS. If the USB cable is connected to the computer, unplug it
before you connect the AI-EXP48.
If you are using the TR-2U external supply (sold separately), connect the power supply to the USB-
1616HS's external power connector, and plug the other end into a power outlet.
The TR-2U is optional, but can be used in any scenario. You may need a TR-2U power supply if the USB
port does not provide enough power for your USB-1616HS application.
The USB-1616HS requires 3000 mW by itself, and 3400 mW when connected to the AI-EXP48.
By USB2 standards, USB 2.0 ports are required to provide at least 2500 mW.
Connect the USB cable to the USB-1616HS USB connector and to a USB port on your computer. A
USB2.0 port is recommended—connecting to a USB1.1 port results in lower performance.
When you connect the USB-1616HS for the first time, a Found New Hardware message opens as the
USB-1616HS is detected. When the message closes, the installation is complete.
The power LED (bottom LED) blinks during device detection and initialization, and then remains solid if
properly detected. If not, check if the USB-1616HS has sufficient power. When the board is first powered on,
there is usually a momentary delay before the power LED begins to blink, or come on solid.
Caution! Do not disconnect any device from the USB bus while the computer is communicating with the
USB-1616HS, or you may lose data and/or your ability to communicate with the USB-1616HS.

USB-1616HS User's Guide Installing the USB-1616HS
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Configuring the hardware
All hardware configuration options on the USB-1616HS are software-controlled. You can select some of the
configuration options using InstaCal, such as the analog input configuration (16 single-ended or 8 differential
channels), and the edge used for pacing when using an external clock. When measuring from thermocouples,
make sure you configure the channels for differential mode.
Once selected, any program that uses the Universal Library initializes the hardware according to these
selections.
Caution! Turn off power to all devices connected to the system before making connections. Electrical shock
or damage to equipment can result even under low-voltage conditions.
Information on signal connections
General information regarding signal connection and configuration is available in the Guide to Signal
Connections. This document is available on our web site at www.mccdaq.com/signals/signals.pdf.
Caution! Always handle components carefully, and never touch connector terminals or circuit components
unless you are following ESD guidelines in an appropriate ESD-controlled area. These guidelines
include using properly-grounded mats and wrist straps, ESD bags and cartons, and related
procedures.
Avoid touching board surfaces and onboard components. Only handle boards by their edges. Make
sure the USB-1616HS does not come into contact with foreign elements such as oils, water, and
industrial particulate.
The discharge of static electricity can damage some electronic components. Semiconductor
devices are especially susceptible to ESD damage.
Connecting the board for I/O operations
Connectors, cables –main I/O connector
The following table lists the board connectors, applicable cables, and compatible accessory products for the
USB-1616HS.
Main connector specifications
Main connectors
Six banks of removable screw-terminal blocks
Expansion connector
25-pin DSUB, female (DSUB25F)
Compatible cable for the 25-pin expansion connector
CA-96A
Compatible accessory product for the 25-pin expansion
connector
AI-EXP48 expansion board with screw terminals (can connect
to the USB-1616HS directly, or with the CA-96A cable)

USB-1616HS User's Guide Installing the USB-1616HS
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Screw terminal pin outs
USB-1616HS screw terminal pin out –single-ended connections
Analog Out
Analog common (A)
Port A
Digital common (D)
DIG-Tmr I/O
NC
FIRSTPORTA Bit 0 (A0)
NC
FIRSTPORTA Bit 1 (A1)
NC
FIRSTPORTA Bit 2 (A2)
NC
FIRSTPORTA Bit 3 (A3)
Analog common (A)
FIRSTPORTA Bit 4 (A4)
CAL (Reserved for self-calibration)
FIRSTPORTA Bit 5 (A5)
Signal ground (S)
FIRSTPORTA Bit 6 (A6)
Digital common (D)
FIRSTPORTA Bit 7 (A7)
TTL trigger (TRG)
Digital common (D)
Output scan clock I/O (DPR)
Timer 0 (T0)
Input scan clock I/O (APR)
Timer 1 (T1)
Analog In
Analog common (A)
Port B
Digital common (D)
Dig-Ctr I/O
CH 0 (0H)
FIRSTPORTB Bit 0 (B0)
CH 8 (8L)
FIRSTPORTB Bit 1 (B1)
Analog common (A)
FIRSTPORTB Bit 2 (B2)
CH 1 (1H)
FIRSTPORTB Bit 3 (B3)
CH 9 (9L)
FIRSTPORTB Bit 4 (B4)
Analog common (A)
FIRSTPORTB Bit 5 (B5)
CH 2 (2H)
FIRSTPORTB Bit 6 (B6)
CH 10 (10L)
FIRSTPORTB Bit 7 (B7)
Analog common (A)
Digital common (D)
CH 7
CH 3 (3H)
Counter 0 (CT0)
CH 11 (11L)
Counter 1 (CT1)
Analog In
Analog common (A)
Port C
Digital common (D)
Dig-Ctr I/O
CH 4 (4H)
FIRSTPORTC Bit 0 (C0)
CH 12 (12L)
FIRSTPORTC Bit 1 (C1)
Analog common (A)
FIRSTPORTC Bit 2 (C2)
CH 5 (5H)
FIRSTPORTC Bit 3 (C3)
CH 13 (13L)
FIRSTPORTC Bit 4 (C4)
Analog common (A)
FIRSTPORTC Bit 5 (C5)
CH 6 (6H)
FIRSTPORTC Bit 6 (C6)
CH 14 (14L)
FIRSTPORTC Bit 7 (C7)
Analog common (A)
Digital common (D)
CH 7 (7H)
Counter 2 (CT2)
CH 15 (15L)
Counter 3 (CT3)

USB-1616HS User's Guide Installing the USB-1616HS
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USB-1616HS screw terminal pin out –differential connections
Analog Out
Analog common (A)
Port A
Digital common (D)
DIG-Tmr I/O
NC
FIRSTPORTA Bit 0 (A0)
NC
FIRSTPORTA Bit 1 (A1)
NC
FIRSTPORTA Bit 2 (A2)
NC
FIRSTPORTA Bit 3 (A3)
Analog common (A)
FIRSTPORTA Bit 4 (A4)
CAL (Reserved for self-calibration)
FIRSTPORTA Bit 5 (A5)
Signal ground (S)
FIRSTPORTA Bit 6 (A6)
Digital common (D)
FIRSTPORTA Bit 7 (A7)
TTL trigger (TRG)
Digital common (D)
Output scan clock I/O (DPR)
Timer 0 (T0)
Input scan clock I/O (APR)
Timer 1 (T1)
Analog In
Analog common (A)
Port B
Digital common (D)
Dig-Ctr I/O
CH 0 HI (0H)
FIRSTPORTB Bit 0 (B0)
CH 0 LO (8L)
FIRSTPORTB Bit 1 (B1)
Analog common (A)
FIRSTPORTB Bit 2 (B2)
CH 1 HI (1H)
FIRSTPORTB Bit 3 (B3)
CH 1 LO (9L)
FIRSTPORTB Bit 4 (B4)
Analog common (A)
FIRSTPORTB Bit 5 (B5)
CH 2 HI (2H)
FIRSTPORTB Bit 6 (B6)
CH 2 LO (10L)
FIRSTPORTB Bit 7 (B7)
Analog common (A)
Digital common (D)
CH 7
CH 3 HI (3H)
Counter 0 (CT0)
CH 3 LO (11L)
Counter 1 (CT1)
Analog In
Analog common (A)
Port C
Digital common (D)
Dig-Ctr I/O
CH 4 HI (4H)
FIRSTPORTC Bit 0 (C0)
CH 4 LO (12L)
FIRSTPORTC Bit 1 (C1)
Analog common (A)
FIRSTPORTC Bit 2 (C2)
CH 5 HI (5H)
FIRSTPORTC Bit 3 (C3)
CH 5 LO (13L)
FIRSTPORTC Bit 4 (C4)
Analog common (A)
FIRSTPORTC Bit 5 (C5)
CH 6 HI (6H)
FIRSTPORTC Bit 6 (C6)
CH 6 LO (14L)
FIRSTPORTC Bit 7 (C7)
Analog common (A)
Digital common (D)
CH 7 HI (7H)
Counter 2 (CT2)
CH 7 LO (15L)
Counter 3 (CT3)
DSUB25F expansion connector
Figure 2. DSUB25 expansion connector pin out

USB-1616HS User's Guide Installing the USB-1616HS
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Cabling
Use a CA-96A 25-pin expansion cable (CA-96A expansion cable) to connect to the USB-1616HS's 25-pin
expansion connector.
Figure 3. CA-96A expansion cable

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Chapter 3
Functional Details
This chapter contains detailed information on all of the features available from the board, including:
a diagram and explanations of physical board components
a functional block diagram
information on how to use the signals generated by the board
diagrams of signals using default or conventional board settings
USB-1616HS components
These USB-1616HS components are shown in Figure 4.
Six removable screw terminal blocks
One USB port
One external power connector
One 25-pin expansion connector
Two LED indicators ("Active" and "Power")
Figure 4. USB-1616HS components –front view

USB-1616HS User's Guide Functional Details
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Figure 5. USB-1616HS components –rear view
External power connector
Although the USB-1616HS is powered by a USB port on a host PC, an external power connector may also be
required to provide sufficient power for the USB-1616HS.
Connect the optional TR-2U power supply to the external power supply connector. This power supply provides
9 VDC, 1 A power to the USB-1616HS.

USB-1616HS User's Guide Functional Details
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USB-1616HS block diagram
Figure 6 shows a simplified block diagram of the USB-1616HS. This board provides all of the functional
elements shown in the figure.
Figure 6. USB-1616HS functional block diagram
Synchronous I/O –mixing analog, digital, and counter scanning
The USB-1616HS can read analog, digital, and counter inputs, while generating two digital pattern outputs at
the same time. Digital and counter inputs do not affect the overall A/D rate because these inputs use no time slot
in the scanning sequencer.
For example, one analog input channel can be scanned at the full 1 MHz A/D rate along with digital and counter
input channels. Each analog channel can have a different gain, and counter and digital channels do not need
additional scanning bandwidth as long as there is at least one analog channel in the scan group.
Digital input channel sampling is not done during the "dead time" of the scan period where no analog sampling
is being done either.
Analog input
The USB-1616HS has a 16-bit, 1-MHz A/D coupled with 16 single-ended, or eight differential analog inputs.
Seven software programmable ranges provide inputs from ±10 V to ±100 mV full scale.

USB-1616HS User's Guide Functional Details
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Analog input scanning
The USB-1616HS has several scanning modes to address various applications. You can load the 512-location
scan buffer with any combination of analog input channels. All analog input channels in the scan buffer are
measured sequentially at 1 µs per channel by default.
For example, in the fastest mode, with ADC settling time set to 1 µs, a single analog channel can be scanned
continuously at 1 MS/s; two analog channels can be scanned at 500 kS/s each; 16 analog input channels can be
scanned at 62.5 kS/s.
Settling time
For most applications, leave the settling time at its default of 1 µs.
However, if you are scanning multiple channels, and one or more channels are connected to a high-impedance
source, you may get better results by increasing the settling time. Remember that increasing the settling time
reduces the maximum acquisition rate.
You can set the settling time to 1 µs, 5 µs, 10 µs, or 1 ms.
Example: Analog channel scanning of voltage inputs
Figure 7 shows a simple acquisition. The scan is programmed pre-acquisition and is made up of six analog
channels (Ch0, Ch1, Ch3, Ch4, Ch6, and Ch7). Each of these analog channels can have a different gain. The
acquisition is triggered and the samples stream to the PC. Each analog channel requires one microsecond of
scan time—therefore the scan period can be no shorter than 6 µs for this example. The scan period can be made
much longer than 6 µs—up to 1 s. The maximum scan frequency is one divided by 6 µs, or 166,666 Hz.
Figure 7. Analog channel scan of voltage inputs example
Example: Analog channel scanning of voltage and temperature inputs
Figure 8 shows a programmed pre-acquisition scan made up of six analog channels (Ch0, Ch1, Ch5, Ch11,
Ch12, Ch13). Each of these analog channels can have a different gain. You can program channels 0 and 1 to
directly measure TCs.
In this mode, oversampling is programmable up to 16384 oversamples per channel in the scan group. When
oversampling is applied, it is applied to all analog channels in the scan group, including temperature and voltage
channels. Digital channels are not oversampled.
If you want 256 oversamples, then each analog channel in the scan group will take 256 µs, and the returned 16-
bit value represents an average of 256 consecutive 1 µs samples of that channel. The acquisition is triggered and
16-bit values—each representing an average of 256—stream to the PC via the USB cable. Since two of the
channels in the scan group are temperature channels, you need the acquisition engine to read a cold-junction-
compensation (CJC) temperature every scan.
Figure 8. Analog channel scanning of voltage and temperature inputs example

USB-1616HS User's Guide Functional Details
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Since the targeted number of oversamples is 256 in this example, each analog channel in the scan group
requires 256 microseconds to return one 16-bit value. The oversampling is also done for CJC temperature
measurement channels, making the minimum scan period for this example 7 x 256 µs, or 1792 µs. The
maximum scan frequency is the inverse of this number, 558 Hz.
For accurate measurements, you must associate TC and CJC channels properly
The TC channels must immediately follow their associated CJC channels in the channel array. For accurate TC
readings, associate CJC0 with TC0, CJC1 with TC1 and TC2, CJC2 with TC3, CJC3 with TC4, CJC4 with TC5
and TC6, and CJC5 with TC7.
When the AI-EXP48 module is connected to the USB-1616HS, associate CJC6 with TC8 through TC11, CJC7
with TC12 through TC15, CJC8 with TC16 through TC19, CJC9 with TC20 through TC23, CJC10 with TC24
through TC27, and CJC11 with TC28 through TC31.
Example: Analog and digital scanning, once per scan mode
The scan is programmed pre-acquisition and is made up of six analog channels (Ch0, Ch2, Ch5, Ch11, Ch13,
Ch15) and four digital channels (16-bits of digital IO, three counter inputs.) Each of the analog channels can
have a different gain.
The acquisition is triggered and the samples stream to the PC via the USB cable. Each analog channel requires
one microsecond of scan time. Therefore, the scan period can be no shorter than 6 µs for this example. All of
the digital channels are sampled at the start of scan and do not require additional scanning bandwidth as long as
there is at least one analog channel in the scan group. The scan period can be made much longer than 6 µs, up to
1 second. The maximum scan frequency is one divided by 6 µs or 166,666 Hz.
Figure 9. Analog and digital scanning, once per scan mode example
The counter channels may return only the lower 16-bits of count value if that is sufficient for the application.
They could also return the full 32-bit result if necessary. Similarly, the digital input channel could be the full 24
bits if desired or only eight bits if that is sufficient. If the three counter channels are all returning 32-bit values
and the digital input channel is returning a 16-bit value, then 13 samples are being returned to the PC every scan
period, with each sample being 16-bits. The 32-bit counter channels are divided into two 16-bit samples—one
for the low word, and the other for the high word. If the maximum scan frequency is 166,666 Hz, then the data
bandwidth streaming into the PC is 2.167 MS/s. Some slower PCs may have a problem with data bandwidths
greater than 6 MS/s.
The USB-1616HS has an onboard 1 MS buffer for acquired data.
Example: Sampling digital inputs for every analog sample in a scan group
The scan is programmed pre-acquisition and is made up of six analog channels (Ch0, Ch2, Ch5, Ch11, Ch13,
Ch15) and four digital channels (16-bits of digital input, three counter inputs.) Each of the analog channels can
have a different gain.
The acquisition is triggered and the samples stream to the PC via the USB cable. Each analog channel requires
one microsecond of scan time therefore the scan period can be no shorter than 6 µs for this example. All of the
digital channels are sampled at the start of scan and do not require additional scanning bandwidth as long as
there is at least one analog channel in the scan group. The 16-bits of digital input are sampled for every analog
sample in the scan group. This allows up to 1 MHz digital input sampling while the 1 MHz analog sampling
bandwidth is aggregated across many analog input channels.

USB-1616HS User's Guide Functional Details
19
The scan period can be made much longer than 6 µs—up to 1 second. The maximum scan frequency is one
divided by 6 µs, or 166,666 Hz. Note that digital input channel sampling is not done during the "dead time" of
the scan period where no analog sampling is being done either.
Figure 10. Analog and digital scanning, once per scan mode example
If the three counter channels are all returning 32-bit values and the digital input channel is returning a 1-bit
value, then 18 samples are returned to the PC every scan period, with each sample being 16-bits. Each 32-bit
counter channel is divided into two 16-bit samples—one for the low word and the other for the high word. If the
maximum scan frequency is 166,666 Hz, then the data bandwidth streaming into the PC is 3 MS/s. Some slower
PCs may have a problem with data bandwidths greater than 6 MS/s.
The USB-1616HS has an onboard 1 MS buffer for acquired data.
Thermocouple input
You can configure up to eight analog inputs in differential mode on the USB-1616HS to accept a thermocouple
(TC) input. Built-in cold-junction sensors are provided for each of the screw-terminal connectors, and any TC
type can be attached to any of the eight thermocouple channels.
When measuring TCs, the USB-1616HS can operate in an averaging mode, taking multiple readings on each
channel, applying digital filtering and cold-junction compensation, and then converting the readings to
temperature.
As a result, the USB-1616HS measures channels with TCs attached at a rate from 50 Hz to 10 kHz, depending
on how much over-sampling is selected.
Additionally, a rejection frequency can be specified in which over sampling occurs during one cycle of either
50 Hz or 60 Hz, providing a high level of 50 Hz or 60 Hz rejection.
The USB-1616HS does not have open thermocouple detection.
Tips for making accurate temperature measurements
Set the rejection frequency to equal the line frequency.
Warm up the USB-1616HS for 60 minutes—including TC wires—so that it is thermally stabilized. This
warm-up time enables the CJC thermistors to more accurately measure the junction at the terminal block.
Make sure the surrounding environment is thermally stabilized and ideally around 20 °C to 30 °C. If the
device's ambient temperature is changing due to a local heating or cooling source, then the TC junction
temperature may be changing and the CJC thermistor will have a larger error.
Use small-diameter, instrument-grade TC wire. Small diameter TC wire has less effect on the TC junction
at the terminal block because less heat is transferred from the ambient environment to the junction.
Use shielded TC wire (see "Shielding" on page 20) with the shield connected to analog common to reduce
noise. The USB-1616HS has several analog commons on the screw terminals.
You can also minimize the effect of noise by averaging readings (see "Averaging" on page 20), or
combining both shielding and averaging.
Refer to "Screw terminal pin outs" section starting on page 11 for the locations of these analog common
screw terminals.
Make sure the USB-1616HS is mounted on a flat surface.

USB-1616HS User's Guide Functional Details
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Be careful to avoid loading down the digital outputs too heavily (>1 mA). Heavy load down causes
significant heat generation inside the unit and increase the CJC thermistor error.
Shielding
Use shielded TC wire with the shield connected to analog common to reduce noise.
The USB-1616HS several analog common screw terminals (see "Connecting the board for I/O operations"
starting on page 10). You can connect the shield of a shielded thermocouple to one of the analog commons.
When this connection is made, leave the shield at the other end of the thermocouple unconnected.
Caution! Connecting the shield to common at both ends results in a ground loop.
Averaging
Certain acquisition programs apply averaging after several samples have been collected. Depending on the
nature of the noise, averaging can reduce noise by the square root of the number of averaged samples.
Although averaging can be effective, it suffers from several drawbacks:
Noise in measurements only decreases as the square root of the number of measurements—reducing RMS
noise significantly may require many samples. Thus, averaging is suited to low-speed applications that can
provide many samples.
Only random noise is reduced or eliminated by averaging. Averaging does not reduce or eliminate periodic
signals.
Digital I/O
Twenty-four TTL-level digital I/O lines are included in each USB-1616HS. You can program digital I/O in
8-bit groups as either inputs or outputs and scan them in several modes (see "Digital input scanning" below).
You can access input ports asynchronously from the PC at any time, including when a scanned acquisition is
occurring.
Digital input scanning
Digital input ports can be read asynchronously before, during, or after an analog input scan.
Digital input ports can be part of the scan group and scanned along with analog input channels. Two
synchronous modes are supported when digital inputs are scanned along with analog inputs. Refer to "Example
4: Sampling digital inputs for every analog sample in a scan group" on page 11 for more information.
In both modes, adding digital input scans has no affect on the analog scan rate limitations.
If no analog inputs are being scanned, the digital inputs can sustain rates up to 4 MHz.
Higher rates—up to 12 MHz—are possible depending on the platform and the amount of data being transferred.
Digital outputs and pattern generation
Digital outputs can be updated asynchronously at anytime before, during, or after an acquisition. You can use
two of the 8-bit ports to generate a digital pattern at up to 4 MHz. The USB-1616HS supports digital pattern
generation. The digital pattern can be read from PC RAM.
Higher rates—up to 12 MHz—are possible depending on the platform and the amount of data being transferred.
Digital pattern generation is clocked using an internal clock. The onboard programmable clock generates
updates ranging from once every 1 second to 1 MHz, independent of any acquisition rate.
Triggering
Triggering can be the most critical aspect of a data acquisition application. The USB-1616HS supports the
following trigger modes to accommodate certain measurement situations.