Measurement WBK40 User Manual

WBK18

Dynamic Signal Conditioning Module

Description…… 1

Current Source with Transducer Fault Detection…… 2
Input Coupling …… 2
Programmable Gain Amplifier (PGA) …… 2
Low-Pass Anti-Aliasing Filter …… 3
Overrange Detection …… 3
Simultaneous Sample and Hold …… 3
TEDS Support …… 4
Excitation Source …… 4
LEDs …… 4

Hardware Setup …… 5

Configuration…… 5
Power…… 5
Assembly…… 6
Input Connections ……6

Description

The WBK18 is a dynamic analog signal input module for the WaveBook data acquisition system. The
WBK18 provides a complete system to interface to piezoelectric transducers that include accelerometers,
microphones, force/pressure transducers, and others.

Software Setup …… 7

General ……7
Maximizing Alias Protection ……9
Using the 2-Pole Filter and Bypass……11
Module Configuration …… 13

Using Accelerometers …… 18

Overview …… 18
Accelerometer Specification

Parameters …… 18
Electrical Grounding…… 20
Cable Driving…… 20

Fuse Replacement …… 22
Specifications …… 24

WBK18, Front and Rear Panel Views

Each WBK18 channel features:

a 4 mA current source for transducer biasing •

•

hardware detection of a transducer fault

•

AC (0.1 Hz or 10 Hz) or DC coupling

•

a programmable gain amplifier (range selection)

•

hardware overrange detection

•

an anti-aliasing low-pass filter

•

a simultaneous sample-and-hold (SSH) amplifier

•

support for optional TEDS (Transducer Electronic Data Sheet), if purchased

All of these parameters are independently controlled in software on a per channel basis except
for overrange detection level, which is set on a per module basis.

WBK18, Dynamic Signal Input Module

WBK18, pg. 1

926896

The WBK18 module includes a built-in programmable voltage excitation source. This source can be used
to stimulate dynamic systems for transfer function measurements, and also serves as a test signal for the
input channels.

WBK18 Block Diagram

Current Source with Transducer Fault Detection

The WBK18 module provides constant current of 4mA to bias ICP transducers. The bias current is sourced through
the center conductor of the input channel BNC connector and returns to the WBK18 by the outer conductor. The
current source features an operating compliance of 24V and is short-circuit and overvoltage protected. Operating
compliance refers to the highest voltage that can be applied without change of the current source value. In the
absence of a transducer, the current source will output an open circuit voltage of 30V. For applications that do not
require bias, the current source can be disconnected from the input via software control on a per channel basis.

When the current source is enabled, the input voltage is continuously monitored with level detection circuitry.
Recognition of a voltage greater than 25V (transducer open) or less than 1V (transducer short) triggers a transducer
fault condition for the affected channel. This error is communicated to the user via a front panel LED and is also
available through a software status request at the end of an acquisition. When recognized, an error is latched until
the commencement of a new acquisition. Consequently, even intermittent faults are detected and communicated.
Detection of a fault does not, however, alter the acquisition process or its data.

Input Coupling

Each WBK18 channel offers the selection of three coupling modes: 0.1 Hz, 10 Hz, or DC. The 0.1 Hz path is a 1­pole high-pass filter with a –3dB point at 0.1 Hz. The 10 Hz path is a 2-pole high-pass filter with a –3dB point at
10 Hz. The DC path provides a direct signal connection.

Programmable Gain Amplifier (PGA)

The WBK18 provides programmable gains of 1, 2, 5, 10, 20, 50, 100, and 200. These correspond to bipolar input
ranges of 5V, 2.5V, 1V, 500mV, 250mV, 100mV, 50mV, and 25mV. Additionally, there is a 25V DC-coupled only
range that is suitable for proximity sensor measurements. Range selection is programmable on a per channel basis.

WBK18, pg. 2

WBK18, Dynamic Signal Input Module

926896

Low-Pass Anti-Aliasing Filter

Each channel features a programmable low-pass filter to provide alias protection and to allow for the removal of
undesired frequencies from the measured response. This filter is configurable within 3 modes: 8-pole, 2-pole, and
Bypass. The 8-pole Butterworth switched capacitor filter offers the greatest alias protection and is most commonly
used in vibration measurements. Its –3dB cutoff frequency is settable from 10 Hz to 50 kHz in a 1-2-5 progression.
Application information regarding the proper setting of this filter is provided in Maximizing Alias Protection.

2-pole mode utilizes two RC filters in series. Its –3dB cutoff frequency is settable as well from 10 Hz to 50 kHz in
a 1-2-5 progression. It provides tighter amplitude and offset accuracy than 8-pole mode at the expense of reduced
alias protection (due to its more gradual roll-off). It is most commonly used in proximity sensor measurements,
where the DC component of the input signal is critical. Additionally, the filter can be bypassed altogether, resulting
in a signal bandwidth of up to 200 kHz.

When the LPF (Low Pass Filter) is in the Bypass mode, the bandwidth of the system depends on the coupling mode
selected. For the 0.1 Hz and 10 Hz selections, the bandwidth is approximately 190 kHz. For the DC selection, the
bandwidth is approximately 130 kHz. For the 25 V range, the bandwidth is approximately 120 kHz.

Reference Note:
Application information regarding the 2-pole and Bypass settings of the filter is provided in the section
entitled, Using the 2-Pole Filter and Bypass (page 11).

Overrange Detection

Each WBK18 channel is equipped with overrange detection circuitry. Use of this feature insures that all data
collected during an acquisition did not exceed a user-specified level, set as a percentage of range. In its most
common use, with the level set to 100%, the user is notified if the input signal exceeded the input full-scale range,
even momentarily. This protection is critical, for overrange signals result in clipped data that significantly corrupts
FFT analysis. This error is communicated to the user via a front panel LED and is also available through a software
status request at the end of an acquisition. When recognized, an error is latched until the commencement of a new
acquisition. Consequently, even intermittent faults are detected and communicated. However, an overrange event
does not stop the acquisition process or change the data, providing the user with full control over the disposition of
data.

An extension of the overrange capability could involve its integration into a process monitor application, whereby
the fault condition is used to monitor the stability of a previously characterized dynamic signal. The overrange level
is programmable from 1 to 100% of range on a per WBK18 basis. Overrange detection can be enabled or disabled
on a per channel basis.

Simultaneous Sample and Hold

All WBK18 channels are sampled simultaneously, after which the WaveBook measures each output until all
channels are digitized. The time-skew between sampling on all channels is 100ns, regardless of the number of
WBK18s connected to the WaveBook. This maximizes channel-to-channel phase matching.

When using WaveBook with an SSH channel enabled, the per-channel sample rates are reduced.
The rate reduction is the same as that which would occur if another channel were added. The
per-channel rate (with SSH enabled) is:

1 MHz / (n+1), where n is the number of active channels.

WBK18, Dynamic Signal Input Module

WBK18, pg. 3

926896

TEDS Support

TEDS, Transducer Electronic Data Sheet, is a purchased option. The TEDS feature enables a WBK18 module to
access the calibration information that is stored within TEDS-compatible sensors. The WBK18 can read calibration
information from sensors and automatically scale the readings from each sensor, using the acquired calibration
information. TEDS support is a software option that can easily be added after the initial purchase of the WBK18.

Reference Note:
Information regarding TEDS in relation to the WaveView software application begins on page 8.

Excitation Source

The WBK18’s AC excitation source is a sine wave-based voltage source that is programmable in frequency from
1 Hz to 5 kHz and in discrete amplitudes from 100 mVp-p to 10 Vp-p. Continuous sine, sweep sine, and custom
sine modes are available. It can be used as a test source for the input channels or as excitation for other system
elements, such as the amplifier for a shaker table. All of its parameters are software controlled, and its output is
conveniently provided on a front panel BNC connection. Detailed information on the excitation source and its
operation can be found in the Software Setup section.

Do not confuse excitation source with the Source Level column in WaveView’s main window, as source level refers
to transducer bias current (see Source Level, page 8) and not to the excitation source.

LEDs

The right-hand side of the WBK18 front panel includes 19 indicator LEDs. There are eight Transducer Fault LEDs
(1 for each channel), eight Overrange LEDs (1 for each channel), an Active LED, Ready LED and a Power LED.
The indicators have the following meanings.

Transducer Fault

(1 LED per Channel)

Overrange

(1 LED per Channel)

Active

Ready

When lit, a Transducer Fault LED indicates that the transducer for the associated channel has
either an open circuit or a short circuit. In addition to LED indication, transducer fault
information is available through a software status request at the end of an acquisition.
Transducer fault errors are latched until the commencement of a new acquisition.
Consequently, even intermittent faults are detected and communicated. Detection of a
transducer fault does not stop an acquisition or alter data. For related information refer to

Current Source with Transducer Fault Detection on page 2.

When lit, an Overrange LED indicates that the associated channel’s input signal has exceeded
the input full-scale range, which was programmed for that specific WBK18 module. Even a
momentary exceeding of the range will cause the LED to light. This indication is critical, for
overrange signals result in clipped data that significantly corrupts FFT analysis. In addition
to LED indication, the overrange condition is available through a software status request at
the end of an acquisition. Overrange errors are latched until the commencement of a new
acquisition. Consequently, even intermittent faults are detected and communicated.
Overrange events do not stop an acquisition or alter data. For related information refer to

Overrange Detection on page 3.

Lights when data is being converted.

Lights when the WBK18 has established communication via its Expansion Control In
connector.

Power

Lights when power to the unit is turned on and present.

WBK18, pg. 4

WBK18, Dynamic Signal Input Module

926896

Hardware Setup

Configuration

The WBK18 requires no physical hardware settings. All WBK18 configurations are controlled by software.

Power

The WBK18 module can be powered by an AC power adapter or directly from any 10 to 30 VDC source, such as a
12 V car battery. For portable or field applications, the WBK18 and the WaveBook can be powered by the
DBK30A rechargeable battery module.

Reference Note:
Setup information pertaining to power, expansion control, and expansion signal connections is
contained in the chapter System Setup and Power Options, in the WaveBook User’s Manual.

It is possible to connect a WaveBook to the host computer’s parallel port with either a 2-foot
(CA-35-2) or 6-foot (CA-35-6) communication cable. To minimize the amount of noise that is
introduced to the WBK18, use of the 2-foot (CA-35-2) cable with the WaveBook is
recommended.

Reference Note:

For details regarding power, refer to the chapter, System Setup and Power Options, in the
WaveBook User’s Manual.

As described in this referenced chapter, it is possible to power the WBK18 from the POWER OUT
DIN5 connector on the WaveBook and to power other WBK expansion modules from the POWER
OUT DIN5 connector on the WBK18. The following notes apply to those types of power connections.

Tables for determining amp load are provided in the WaveBook User’s Manual chapter entitled
System Setup and Power Options. The following factors are very important.

Calculate system amp load prior to creating a system daisy-chain. Although WaveBook

•

device connectors and CA-115 power cables have 5 amp limits, TR-40Us are limited to

2.2 amps. If necessary use auxiliary or high-current power supplies.

If using an AC power adapter for the system power, use separate adapters for the

•

WaveBook and the WBK18.

The WBK18 has a 5 amp current limit. TR-40U power supplies are limited to 2.2 amps.

•

Power consumption calculations must be done to ensure that a particular daisy-chain
scheme does not exceed either of these current limits.

WBK18, Dynamic Signal Input Module

WBK18, pg. 5

926896

To ensure that the software recognizes all system components, when powering up an Ethernet
connected WaveBook system, it is important that the WaveBook/516E (or WBK25) is powered
last, and that the most remote system components are powered first. Other power-up sequences
will result in software’s failure to recognize all components.*

*An exception to this power-up scheme is to power-on the entire system at once.

Assembly

The WBK18 has the same footprint as the WaveBook and other modules, allowing for convenient mounting. A
fastener panel allows multiple units to be stacked vertically. Screw-on handles are available for portable
applications. For more assembly information, see chapter 3 of the WaveBook User’s Manual (p/n 489-0901).

Input Connections

All input connections are made into the front panel BNCs, in which the BNC center conductor is the signal HI and
the BNC shell is the signal LO. The BNC shell is common among all eight input channels and is not isolated
earth ground. Consequently, the shell is not meant to be driven with respect to earth ground. An additional
consideration exists regarding the setup of the input transducer. If the transducer case is effectively earth grounded
through its connection to a device under test, there exists the possibility for added measurement noise due to the
ground loop that is created. This issue is minimized by electrically isolating the transducer from the device.

First, power-on the WBK expansion modules.

•

•

Second, power-on WaveBooks or WBK modules that are connected to the expansion
ports of the WaveBook/516E or WBK25.

Finally, power-on the WaveBook/516E and/or WBK25 devices.

•

from

CAUTION

The BNC shell is not to be driven with respect to earth ground. Attempting to do so could result
in equipment damage.

Additional measurement noise may be present when using earth grounded transducers.
For best results, electrically isolate the input transducers from earth ground.

WBK18, pg. 6

WBK18, Dynamic Signal Input Module

926896

Software Setup

General

Depending on your application, you will need to set several software parameters. Proper settings will
allow WaveView to organize data to meet your requirements. Some items of importance to the WBK18 are
the low-pass and high-pass filter options that can be selected from the WaveView Configuration main
window and the excitation source and overrange detection parameters that can be chosen from the
Module Configuration window. The Module Configuration window can be accessed from the View pull­down menu or by use of the first toolbar button (located just below the File pull-down menu).

Reference Note:
For detailed WaveView information, refer to the WaveView Document Module.

WaveView Configuration Window

In the WaveView Configuration main window (see figure) the following columns are applicable to the WBK18.

LPF Mode – Click on a cell in the LPF Mode column to make the cell active, and then change its setting. Options
for WBK18’s LPF Mode are:

(a) 8-Pole: selects the 8-pole low-pass filter
(b) 2-Pole: selects the 2-pole low-pass filter
(c) Bypass – bypasses the low-pass filter

LPF Cutoff - Click on a cell in the LPF Cutoff column to make the cell active, and then change its setting. Options
for LPF Cutoff (in Hz) are: 10, 20, 50, 100, 200, 500, 1000, 2000, 5000, 10000, 20000, and 50000. Note that when
the LPF Mode is “Bypass,” this parameter is fixed at 200000 Hz.

Reference Note:
Application information regarding the proper setting of LPF Mode and LPF Cutoff is provided in the
sections entitled Maximizing Alias Protection (page 9) and Using the 2-Pole Filter and Bypass (page 11).

HPF Cutoff - This is used to select input coupling. Click on a cell in the HPF Cutoff column to make the cell
active, and then change its setting. Options for HPF Cutoff are:

(a) 0.1 Hz: selects the 0.1 Hz, 1-pole high-pass filter
(b) 10 Hz: selects the 10 Hz, 2-pole high-pass filter
(c) DC: selects DC coupling

Note that when the Range is “±25V,” the HPF Cutoff is fixed at DC.

Range - This is used to select the input range. Click on a cell in the Range column to make the cell active, and
then change its setting. Options for Range are: ±25V, ±5V, ±2.5V, ±1V, ±500mV, ±250mV, ±100mV, ±50mV,
and ±25mV. Note that when the Range is “±25V,” the HPF Cutoff is fixed at DC.

WBK18, Dynamic Signal Input Module

WBK18, pg. 7

926896

Source Level – Source Level refers to the transducer bias current and is not to be confused with the
excitation source that is discussed on pages 4 and 14. The current Source Level column of WaveView’s
main window is used to turn the transducer bias current on at a current value of 4 mA,
or to turn the transducer bias current off. Click on a cell in the Source Level column to make the cell
active, and then change its setting to 4 mA or to off, according to the application. If a channel is
connected to a transducer that requires a current source, set the source level to 4 mA; otherwise set the
source level to off.

TEDS (Transducer Electronic Data Sheet)

TEDS is a purchased option that enables WBK18 modules to access calibration information from TEDS-compatible
sensors. The WBK18 automatically scales the readings and sets the range according to the information stored on the
sensor. This is done independently for each TEDS associated channel, providing that “Yes” appears in the TEDS
Data cell (right-hand column, following figure).

WaveView Configuration Window

If no WBK18 channels are connected to a TEDS sensor, the entire TEDS
Data column, including the heading, will be grayed-out. When a channel
does have a TEDS sensor it will have an associated cell. You can click on
the cell to access the “Use TEDS Data” pull-down list, which offers 3
choices: No, Yes, and Show.

“No” instructs WaveView not to use TEDS. When TEDS is not used

•

the associated channel will use the default range and units of volts
(V).

“Yes” instructs WaveView to use TEDS. The channel’s ranges will

•

be automatically scaled according to the TEDS sensor’s calibration
data and the units will appear as “g.”

“Show” accesses an Accelerometer TEDS Information box for the

•

associated channel. An example is provided to the right. The
channel, in this case channel 9, is identified in the title bar. When the
information box is closed the TEDS Data cell will indicate its
previous status of Yes or No.

If you add, remove, or relocate a TEDS sensor at the WBK18 channel inputs, the TEDS information,
and WaveView’s range and units will not reflect the change until either (a) the WaveBook is
reselected as a device, or (b) WaveView is closed and then reopened.

WBK18, pg. 8

WBK18, Dynamic Signal Input Module

926896

Accelerometer TEDS Information Box