DT8837

High Performance Ethernet Instrument
Module for Sound & Vibration
Overview
The DT8837 is a high-accuracy, multi-channel modulethat is ideal for sound and vibration measurements.
All the I/O channels are completely isolated from eachother and from the computer, allowing noise-free data
to be sampled in tough industrial environments. Four
24-bit IEPE (ICP®) sensor inputs, a 24-bit D/A stimulus
output, a 31-bit tachometer channel are synchronized toprovide data streams that are matched in time for fieldor laboratory use.

The DT8837, a 1U 1/2 rack instrument module, uses
direct BNC connections to the four parallel ISO-Channel
analog inputs and the analog output. Connections for thetachometer, counters, digital output, and Ethernet areavailable on the rear panel.

The DT8837 offers a readback analog output channel
in the analog input data stream and provides special
measurement modes for precisely correlating thetachometer input with the A/D sensor measurements.
The TCP/IP Ethernet operation allows measurements tobe monitored locally or at other remote sites. Up to 16
instrument modules maybe stacked for parallel operationof 64 accelerometer or voltage inputs. These modules
are synchronized via the Wired Trigger Bus and can be
externally triggered in various ways.
All inputs use ISO-Channel technology, meaning that the
4 IEPE analog inputs, the analog output, tachometer,and 4 robust digital outputs, are galvanically isolated up
to ±500 V from each other and allow a separate returnfor each signal. This protection mechanism guarantees
freedom from ground loops and noise.

Up to 16 modules can be used in parallel to connect up to
64 direct voltage or IEPE channels, each synchronized in amaster/slave configuration. The picture above shows four
instrument modules in such a configuration.

Key Features• IEPE or Voltage inputs

Summary of Features
Analog Input

oo ISO-Channel™ provides ±500 V galvanic isolation

channel-to-channel for all I/O signals andgrounds
oo 4 Simultaneous, 24-bit Delta-Sigma A/D channels
for high resolution measurements, or use as 4
IEPE inputs for direct sensor connection
oo Input range of ±10 V with gains of 1 and 10,
software selectableoo 4 mA current source with 24 V compliancevoltage, software selectableoo AC/DC coupling, software selectable
oo Sample rate up to 52.734 kS/s per channel,
software-selectable• Total In Sync Data
oo ADCs, tachometer, counter and DAC feedback
channels sampled simultaneously and can beselectively included in input sample dataoo Two 32-bit counters for measuring tachometer,gate and ADC conversion relationships



AC/DC/4 mA

Maximum Sample Rate/Channel
1 Tachometer

Up to 52.7 kS/sTachometer Measurement Modes

3

Simultaneous with Analog Output

Analog Output
1 Isolated Channel (ISO-Channel)
24-bit Resolution
Update Rate
Max Update Rate/Channel

Features continued on page 2(508) 946-5100

4 Isolated Channels (ISO-Channel)
24-bit Resolution1Software-selectable
Up to 52.7 kS/s

Buffer Mode

Simultaneous with Analog Input

4 Isolated Digital Outputs, ±30 V @ 400 mA

External Trigger

Multiple Module Synchronization



Ethernet, TCP/IP

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Key Features (continued from page 1)• Continuous Waveform Output• Module Expansion

oo One 24-bit D/A Converter, ±10 voltsoo Onboard memory allows continuous waveformoo Stack up to 16 modules for parallel operation of

64 channels (IEPE or voltage) via the Trigger Bus

output without host communication(2 kilosamples – 128 kilosamples)oo Update rate up to 52.734 kS/s per channel,
software-selectableoo 16-bit feedback ADC to allow correlation of
output stimulus with sampled input data
• Robust Digital Outputs
oo 4 digital outputs can switch up to ±30 V @ 400
mA deal for driving mechanical relays or motors

oo Several Trigger options: Software, External TTL

trigger input, Variable threshold trigger, Trigger
Bus, LAN Trigger Packet
oo Synchronization reference clock, ADC sync andtrigger I/O using Trigger Bus for synchronizing
multiple up to 16 instrument modules

Supported Operating Systems• Windows® 10/8/7/Vista®/XP 32/64-bit+24 Volts
Compliance

4mA IEPE Current Source
24-BitA/D
1M
Analog Input

AC-DC
Coupling

BNC 1±500 V+/-500 Volts
Galvanic Isolation

x1 / 10External
Power+24 Volts
Compliance

Input
FIFO

4mA IEPE Current Source
24-BitA/D
1M
Analog Input

AC-DC
Coupling

BNC 2

ISO-Channel
Inputs±500 V

PLL
ProgrammableClock

x1 / 10

RJ-45

Ethernet
10/100Base-TInterface

Status LEDs

RESET

TM

4mA IEPE Current Source
24-BitA/D
1M
Analog Input

AC-DC
Coupling

BNC 3±500 V

External Trigger±250 V

4mA IEPE Current Source
24-BitA/D
1M
Analog Input

AC-DC
Coupling

BNC 4

10kHz
FilterTM

31-BitTachometer& 2 Counters±500 V

15 Pin D
Conn±250 Vx1 / 1024-Bit D/AConverter

Analog Output

BNC

Timing& Control

x1 / 10+24 Volts
Compliance

ISO-Channel
Output

Wired
TriggerBus(WTB)+24 Volts
Compliance

16-Bit A/DConverter±250 V±500 V

Wave
SampleBuffer±500 V

Clock

DigitalOut

Up to ±30V @ 400mA

LegendGalvanic Isolation

Readback Channel

The design of the DT8837 incorporates galvanically isolated channels, the wired trigger bus for synchronizing acquisition on
multiple instrument modules, and full Ethernet (LXI) compatibility.

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• +5 V power input• instrument moduledraws <6 W
• runs cool withoutfans
Power switch,
ON/OFF
Reset forconvenient
rebootRJ-45 LAN
connector forcomplete TCP/IP
compatibility

Dual 25-pin micro
D connector and
LVDS transceivers for
Wired Trigger Bus

4 individually isolated (±250 V) solidstate relay digital outputs for driving
AC or DC relays directly, capable ofswitching up to ±30 V at 400 mA
15-pin D shell connector fortachometer, 2 counter/timers, 4
isolated relay digital out, external
trigger

Ethernet ARM
processor,
memoryTiming & Control

FIFO for DAC,
and wave sample
buffer for stimulus
waveform(on back)
Isolators foranalog data
provide ±500 V
galvanic isolation

10 kHz filter
prevents higher
frequency noisefrom D/A output

Isolation for IEPE
control, AC-DC
coupling & gain
amplifiers(on back) IEPE highvoltage compliant
current source – up
to 24 V @ 4 mA

(on back) DC-DC
converters forgraceful power
control
4 individual BNC
ISO-Channel
analog inputs

Detailed circuit picture with callouts.

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ISO-Channel
Analog output(stimulus)(on back) Readback
A/D for exact
synchronization of
analog input with
D/A stimulus

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Analog Inputs

Tachometer Input

The DT8837 instrument module supports four, differential
analog input channels. All analog input channels are
simultaneously clocked. The DT8837 instrument module
uses 24-bit Delta-Sigma analog-to-digital converters(ADCs) that provide anti-aliasing filters based on the clock
rate. These filters remove aliasing, which is a condition
where high frequency input components erroneously
appear as lower frequencies after sampling. In addition,
the DT8837 instrument module can acquire data from atachometer, two counter/timers, and the analog output
readback channel.

The DT8837 accepts one 31-bit tachometer input signal
on the input/output connector. You can measure thefrequency or period of the tachometer input signal
by reading the value of the tachometer input channel
in the analog input stream. The frequency or period
measurement allows you to calculate the rotation
speed of tachometer input signals. The tachometer isimplemented with a 32-bit counter/timer, however, themeasurement is contained in the lower 31 bits; the 32nd
bit (MSB) is used as a data flag to indicate new or old
data.

Analog Inputs with IEPE Functions

Counter Input Channels

Applications that require accelerometer, vibration, noise,or sonar measurements often use IEPE sensors. IEPE
conditioning is built-in to the analog input circuitry of
the DT8837 instrument module. The instrument module
supports the following software-programmable IEPE
functions for each of the four analog inputs:

The DT8837 provides two 32-bit counter channels
that can be read as part of the analog input stream.
The counters help the user correlate the analog input
with digital positional input. They can measure thetime between the selected rising or falling edge of thetachometer or gate input or of an ADC conversion andthe selected rising or falling edge the tachometer or gate
input or of an ADC conversion.

• Excitation current source – You can enable ordisable the use of a 4 mA current source with 24 V
compliance voltage to allow wide dynamic range
without distortion. By default, the excitation current
source is disabled.
• Coupling type – You can select whether AC couplingor DC coupling is used. By default, DC coupling isselected.
Break detection is provided if using DC coupling with the
4 mA excitation current source and the voltage input ispositive, full scale.

Input Buffers
The DT8837 uses an 8 MB input buffer for storing datafrom each of up to 8 enabled input channels (analog
input channels 1, 2, 3, 4, tachometer input channel,
counter/timer 1, counter/timer 2, and the analog output
readback channel). One sample from each of the enabled
input channels is called a scan.
You can specify one of the following wrap modes for the
input buffer:

Delta-Sigma A/D Converters• Continuous wrap mode – Use this mode if you want

The DT8837 instrument module includes a 24-bit DeltaSigma ADC for each analog input channel. With built-in
anti-aliasing filters, Delta-Sigma ADCs offer superior AC
performance in noise and vibration applications

the input operation to continue indefinitely. In thiscase, when the end of the input buffer is reached,
the operation wraps to the beginning of the input
buffer overwriting the oldest scan data with thelatest scan data.
• No wrap mode – Use this mode if you want the
input operation to stop automatically when the
input buffer is filled.

Advantages include:• Reduced noise and improve accuracy byoversampling each input• Eliminates errors that result from aliasing and highfrequency noise

Since the maximum input buffer size is 8 MB andeach sample is 4 bytes, you can store a maximum of
2M samples in the input buffer. If you sample each input
channel at the maximum input frequency (52.734 kHz),the input buffer will fill in approximately 5 seconds(52 kS/s per channel).

• Provides excellent low-level signal-to-noise
performance, which improves dynamic accuracy on
low level signals• Provides excellent differential linearity, which
ensures consistently accurate data conversion acrossthe full input range

The maximum size of data transfer over Ethernet is 32 kB.
Since each sample is 4 bytes, the maximum number ofsamples is 8 kilosamples. Therefore, if you are using
continuous wrap mode, ensure that you use a tight loop
to ensure that you retrieve all the samples in the input
buffer before the buffer is overwritten.
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ISO-Channel Front End Design Yields Strong User Advantages
Many industrial environments present noise conditions that are very challenging in achieving precise
measurements. Each ISO-Channel input is designed to isolate it from any other input or any other return path.
It has its own signal return that is referenced to its input signal. Therefore, analog input 1 has its analog return
1. This means that other “grounds” or return paths from other signals or from the computer have no ability tointerfere with an ISO-Channel input and return.
A single ISO-Channel analog input is shown in Fig 5. The input protection circuitry is for ESD prevention. Thena signal path provides direct DC connection or AC coupling via a software-enabled opto-analog switch. This
enables a noise-free switching mechanism.
Direct IEPE connections are achieved through a stable, precision current source of 4 mA with 24 V compliance.
This allows accelerometers for vibration measurements to be directly connected to the analog input and easily
measured.
At the input to the auto-zero amplifier a low frequency pass filter allows signals down to 0.1 Hz to pass formeasuring seismic or low frequency vibration. The signal from the analog input is converted with a 24-bit sigma
delta A/D using a precision voltage reference, accurate to 8 ppm per degree C. This reference is stabilized fromany voltage variances. The sigma delta A/D is used to prevent anti-aliasing by preventing unwanted harmonics.
The analog input to the 24-bit A/D is referenced to the signal return. It is then isolated from the PC ground andother returns through an inductive isolator.

Stable, Precision
Current Source
4mA @ 24V

ESD Protection

Precision
Reference

AnalogInput

ISO-Channel

AC-DC
Coupling

24-bitSigma-Delta
A/D

Isolation

Isolated
Power
Supply

DC-DC

Auto
Zero
Amp

AnalogReturnSync toMasterClock

Signal Bandwidth Response-3dB

A single ISO-Channel path. There are
four ISO-Channel analog inputs andone ISO-Channel analog output.
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The DT8837 provides software selectable AC and DC coupling. When AC coupling is selected, the modules provide zero ripple
in the wide pass band and excellent “brick wall” anti-alias filters eliminating unwanted high frequency interference.

Input Triggers

You can specify one of the following wrap modes for the
output buffer:

A trigger is an event that occurs based on a specified setof conditions. Acquisition starts when the instrument
module detects the initial trigger event and stops wheneither the input buffer has been filled or you stop theoperation. The DT8837 instrument module supports
the following trigger sources for starting analog input
operations: Software trigger , External digital (TTL)
trigger, Analog threshold trigger, Trigger Bus, and LAN
Trigger Packet.

• Continuous wrap mode – Use this mode if you want
the output operation to continue indefinitely. In thiscase, when the end of the output buffer is reached,
the operation wraps to the beginning of the output
buffer overwriting the oldest scan data with thelatest scan data.
• No wrap mode – Use this mode if you want theoutput operation to stop automatically when thenumber of samples specified has been written to theanalog output channel.

Analog Output Channels

Reading the Analog Output Value in the
Analog Input Data Stream

The DT8837 instrument module supports one 24-bit
analog output channel. You can read back the value ofthe analog output channel through the analog input
channel list. A two-pole, 10 kHz Butterworth filter isapplied to prevent noise from interfering with the output
signal. The analog output channel powers up to a valueof 0 V ±10 mV.

You can read back the value of the analog output
channel in the analog input data stream. Specify channel
8 in the analog input channel list to read back the valueof the analog output channel. The software automaticallysynchronizes the value of the analog output channel
with the analog input measurements, so that allmeasurements are correlated in time.

Output Buffers
The DT8837 uses a 128K sample output buffer (alsoknown as a hardware FIFO) for storing analog output
data to write to the analog output channel.
You can specify the number of samples to output to theanalog output channel using software. This value canrange between 1 and 131072.

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Tachometer Edge

A/D ClockRotating Device
Connected to
Tachometer
Input Signal

Signal from analog input ch 1

A/D Clockt2

A/D ClockY
t1

Tacho Pulse
X

New period
measurement Y
available(tachometeredge)

A/D Sample that you
want to correlate withrotation data

New period measurement resultin input data streaming
X

t1
Period measured Tachometer input (1 revolution)

Time

t2
A/D sampling rate 50 KHz (A/D conversion done) or 20 μsec

By connecting a rotating device to the tachometer input of the DT8837, you can measure the frequency or period of therotating device. The DT8837 also provides the ability to accurately measure the time between the tachometer edge and thenext A/D sample or between the A/D sample and the next tachometer edge, so that you can precisely correlate A/D data withrotation data.
For example, assume that you want to correlate A/D sample X from analog channel 1 to an angular position of the rotating
device. This can be accomplished by using a tachometer signal that always occurs at the top, center position of the rotating
device as a reference and measuring the time between the tachometer signal and the next A/D sample (Y). Since you know
the frequency of the A/D sample clock (50 kHz, in this case), you know when A/D sample X occurred in relation to A/D sample
Y (t2 = 1/50 kHz x num samples from Y to X). By using Counter 1 to measure the time (t1) between the tachometer signal andA/D sample Y, you can calculate exactly where A/D sample X occurred in time from the tachometer signal (result = t1 + t2).
Given the rotation speed of Tachometer input, you can then calculate the angular position of A/D sample X.

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The 4 isolated digital outputs offer high drive capability. They are solid state relays that are capable of switching up to±30 V @ 400 mA. Either AC or DC can be switched. The internal solid state relays are poly fused to prevent any damage
and they restore as soon as a short is removed

Output Triggers

Unlike when synchronizing the clock of multiple
instrument modules, which requires one instrument
module dedicated as the clock master, you can have morethan one trigger master, if desired, to trigger multiple
instrument modules. Additionally, the trigger masterneed not be the clock master (for example, a device
other than the DT8837 can generate the trigger for theDT8837 instrument modules, if desired). Figure 11 shows
an example of using two DT8837 trigger masters on the
Trigger Bus.

A trigger is an event that occurs based on a specified
set of conditions. The analog output operation starts
after the trigger is received and stops when either the
specified number of samples have been output or you
stop the operation.
The DT8837 instrument module supports the following
trigger sources for starting analog output operations:
Software trigger, External digital (TTL) trigger, Analog
threshold trigger, Trigger Bus, and LAN Trigger Packet.

Synchronizing Acquisition on Multiple
Instrument Modules

Daisy-Chain Configuration

Up to 16 instrument modules can be connected together
using the Trigger Bus. Multiple DT8837 modules may beconnected using a daisy-chain configuration, using the25-pin Trigger Bus connectors (see figure 9).
When multiple instrument modules are connected
together using the Trigger Bus, as shown in Figure 10,
you can synchronize the start of acquisition using the
LXI7 clock signals, LXI sync signal, and one of six LXI
trigger signals: LXI0 to LXI5.
On the clock master, use software to set the clock source
to internal and to drive out the LXI7 clock signal and LXI6
synchronization signal on the trigger bus.

Trigger Bus Terminators

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DT8837
Slave 1

DT8837
Trigger Master
Trigger Source =Software, Digital,
Threshold,
LAN Trigger
Packet

LXI0-LXI5
Trigger
Enabledand Driven

Trigger Source =LXI0, LXI1, LXI2,
LXI3, LXI4,
or LXI5

LXI6 - Sync
Clock Source =Internal

LXI7- Clock

LAN Trigger Packets

DT8837
Slave n

LXI0-LXI5

When multiple DT8837 instrument modules areconnected together over the local area network (LAN),as shown in Figure 12, Synchronizing the Start ofAcquisition When Triggering you can synchronize thestart of acquisition by transmitting one of eight LAN
trigger packets (LAN0 to LAN7) over the network.

Trigger Source =LXI0, LXI1, LXI2,
LXI3, LXI4,
or LXI5

LXI6 - Sync
Clock Source =LXI7

LXI7- Clock

Clock Source =
LXI7

LAN

Synchronizing the Start of Acquisition When Connecting
Multiple Instrument Modules to the Trigger Bus

On the trigger master, use software to set the trigger
source to software trigger, external digital trigger, analog
threshold trigger, or LAN trigger packet (LAN0 to LAN7).
Then, use software to drive out the LXI trigger signal(LXI0 to LXI5) on the Trigger Bus.

DT8837 #1

DT8837 #2

DT8837 #3

DT8837 #4

Synchronizing the Start of Acquisition When Triggering
Instrument Modules Over the LAN

While a trigger master can drive out more than one
trigger signal on the Trigger Bus, the slave can accept
only one trigger signal to start the analog input
operation. On each slave, use software to select the clock
source as LXI7 and the trigger signal (LXI0 to LXI5) thatwas driven out by the trigger master on the Trigger Bus.

An Example of Using Two Trigger Masters on the Trigger Bus

Once the master is triggered, the specified LXI trigger
signal is driven out on the Trigger Bus to all slaves thatwere configured to accept it. Acquisition starts on thefirst sample after the trigger is received.

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QuickDAQ with Advanced FFT Analysis Option.

QuickDAQ
QuickDAQ allows you to acquire and display from all Data
Translation USB and Ethernet data acquisition devices
that support analog input streaming. Combine QuickDAQ
with Data Translation hardware to acquire data, record
data to disk, display the results in both a plot and digital
display, and read a recorded data file. Be productive rightout of the box with this powerful data logging software.
Data can be exported to other applications like Microsoft
Excel® and The Mathworks MATLAB® for more advanced
analysis. Two additional options can be purchased to add
FFT analysis capabilities to the base package.

oo Supports Hanning, Hamming, Bartlett, Blackman,

Blackman Harris, and Flat Top response windows• Advanced FFT Analysis Option (License Required)oo Includes all the features of the QuickDAQ Base

Package and FFT Analysis Package
oo Perform 2-channel FFT operations including:◊ FRF◊ Cross-Spectrum◊ Cross Power Spectral Density◊ Coherence◊ Coherent Output Poweroo Supports real, imaginary, and Nyquist display

Key Features

functions• QuickDAQ Base Package (Free)

oo Additional FFT analysis functions supported:

Exponential, Force, Cosiner Taper

oo Ready-to-measure application software
oo Configure, acquire, log, display, and analyze youroo Save data to .uff file format

data
oo Customize many aspects of the acquisition,

display, and recording functions to suit yourneeds
• FFT Analysis Option (License Required)oo Includes all the features of the QuickDAQ Base
Packageoo Perform single-channel FFT operations including:◊ Auto Spectrum◊ Spectrum◊ Power Spectral Density
oo Configure and view dynamic performancestatistics(508) 946-5100

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Other Software Options

Ordering Summary

The following software is available for use with the DT8837 Instrument
module and is on the CD included with your hardware:

HARDWARE• DT8837• Eureka Discovery Utility — This utility helps you locate or “discover”
all LXI (Ethernet) instruments that are connected to your system andprovides the following information about your instrument: the IP
address, manufacturer, model number, serial number, and version of
the firmware that is running on your instrument. In addition, you can
use this utility to configure Windows firewall settings and update thefirmware for your Data Translation LXI instrument.
• Instrument Module Web Interface — This built-in interface, allows
you to verify the operation of your DT8837 instrument module andperform basic functions with Internet Explorer and no additional
software. Using it, you can configure your instrument module, control
output signals, measure input signals, and save results to disk.
• DT8837 IVI-COM Driver — This driver provides access to the DT8837
instrument module functions through a COM server. The IVI-COM
driver works in any development environment that supports COM
programming, including Measure Foundry, MATLAB, Visual Basic.NET,
Visual C#.NET, Agilent VEE Pro, LabVIEW, LabWindows, and others.
• SCPI commands — Use network sockets to program and control
LXI Instruments by sending SCPI commands. Refer to the SCPI
Programmer’s Manual for the DT8837 (UM-23333) for information on
the supported SCPI commands and example programs.

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DT8837-Datasheet		11

ACCESSORIES• EP377 Trigger Bus cables (25-pin, .5M)
• EP379 Dual-Rack mount kit• EP380 Single-Rack mount kit
FREE SOFTWARE• QuickDAQ
OPTIONAL SOFTWARE• QuickDAQ FFT Analysis Option (License
Required)• QuickDAQ Advanced FFT Analysis Option(License Required)info@mccdaq.com

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June 2017. Rev 3© Measurement Computing Corporation