CWE BMA-400 User manual
BMA-400
4-Channel Bioamplifier
©CWE 2023
Read instructions carefully before operating this device.
This device is not to be used for Human Life Support applications.
To avoid possible electrical shock, do not operate this device if is wet or has had liquids spilled onto it.
Service or calibration procedures should only be performed by qualified personnel familiar with the
electrical hazards of line-powered devices.
Instruction Manual
www.cwe-inc.com
BMA-400 Instruction Manual 2
© 2023 CWE, Inc.
STATEMENT OF WARRANTY
IF THIS INSTRUMENT FAILS WITHIN A PERIOD OF ONE YEAR FROM THE DATE OF
DELIVERY OR INSTALLATION, CWE, INC. WILL, AT ITS OPTION, REPAIR OR REPLACE
IT FREE OF CHARGE TO THE PURCHASER. THIS WARRANTY EXCLUDES DAMAGE
INCURRED THROUGH ABUSE OR ACCIDENT AND CONSUMABLE ITEMS OR
COMPONENTS SUCH AS BATTERIES. CWE, INC. DOES NOT ASSUME ANY LIABILITY
FOR ANY CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF
THIS INSTRUMENT. THIS WARRANTY IS APPLICABLE ONLY TO THE ORIGINAL
PURCHASER OF THE INSTRUMENT AND IS NON-TRANSFERRABLE.
IF YOU HAVE A PROBLEM
Please call or write describing your problem. We can often identify what iswrong and suggest
a solution without recourse to returning the device. Defective units under warranty should be
returned to the factory along with a note describing the nature of the fault. Every effort will be
made to ensure prompt repair or replacement of the device.
FACTORY SERVICE
Out of warranty or damaged instruments may be returned to the factory postage prepaid for
service at prevailing rates. Upon request, a written or verbal quotation for such service will
be issued after examination of the unit but prior to commencing repairs or service. Please
contact us to obtain an RMA number before returning anything. Address requests for service
or technical information to:
CWE, Incorporated
Technical Support Department
TEL (610)642-7719
LIFE SUPPORT POLICY
INSTRUMENTS MANUFACTURED BY CWE, INCORPORATED ARE NOT AUTHORIZED
FOR USE AS CRITICAL COMPONENTS IN HUMAN LIFE SUPPORT DEVICES OR
SYSTEMS. "LIFE SUPPORT DEVICES OR SYSTEMS", AS USED HEREIN, ARE DEVICES
OR SYSTEMS WHOSE FAILURE TO PERFORM, WHETHER THROUGH MISUSE,
FAILURE, OR PROPER OPERATION, CAN REASONABLY BE EXPECTED TO RESULT
IN SIGNIFICANT INJURY TO THE OPERATOR OR SUBJECT PERSONS.
This document last updated 5/12/23
BMA-400 Instruction Manual 3
© 2023 CWE, Inc.
TABLE OF CONTENTS
1.0 INTRODUCTION..............................................................................................................4
Figure 1: BMA-400 front panel .....................................................................................3
2.0 SPECIFICATIONS...........................................................................................................5
3.0 POWER SUPPLY CONNECTION....................................................................................5
4.0 INPUTS............................................................................................................................6
4.1 INPUT CONNECTOR WIRING.................................................................................6
Figure 2: BMA-400 Input Connector Wiring...................................................................6
5.0 AMPLIFIER CONTROLS .................................................................................................7
Figure 3: Front panel controls (one channel shown)........................................................7
5.1 AC/DC COUPLING ...................................................................................................7
5.2 GAIN CONTROL.......................................................................................................8
5.3 FILTERS...................................................................................................................8
5.31 LOW FREQUENCY FILTER SWITCH (Outer Knob)........................................8
5.32 HIGH FREQUENCY FILTER SWITCH (Inner Knob)........................................8
Table 1: Bandpass settings for typical applications ..................................................8
5.4 INDICATOR LIGHTS.................................................................................................9
6.0 OUTPUT (Rear Panel).....................................................................................................9
7.0 STIM/RECORD FUNCTION.............................................................................................9
8.0 DATA PORT CONNECTOR (REAR PANEL).................................................................10
Figure 4: DATA PORT connections..................................................................................10
9.0 SETTING THE DC OFFSET RANGE.............................................................................10
10.0 OPTIONAL HEAD-STAGES.........................................................................................11
11.0 USING TRANSDUCERS WITH THE BMA-400............................................................11
12.0 ORDERING INFORMATION........................................................................................12
BMA-400 Instruction Manual 4
© 2023 CWE, Inc.
1.0 INTRODUCTION
The BMA-400 Bioamplifier is a four-channel AC/DC preamplifier for the low-noise recording
of muscle, nerve, or other biopotentials. The wide gain range of the BMA-400 allows its use
as a primary amplifier whose output can be fed directly to data acquisition systems or
oscilloscope displays. The six-position high and low pass filters have a sharp roll off for
limiting the signal to the desired frequency bandwidth. The frequency response of the BMA-
400 covers the range DC-50kHz. Provision is made for passing external stimulus currents
to the electrodes. A full range of head-stages and electrode connectors is available,
including a medical-grade isolation amplifier head-stage suitable for safe human subject
recording.
Figure 1: BMA-400 front panel
BMA-400 Instruction Manual 5
© 2023 CWE, Inc.
2.0 SPECIFICATIONS
Input type .......................................................... differential instrumentation amplifier
Input impedance ................................................................................... >10,000 M
Input connector ................................................. 7-pin Amphenol 703-91T-3475-001
Noise, wideband, referred to input........................................... <7V P-P, <3V RMS
Common mode rejection ................................................................ >100dB @ 60Hz
Input voltage range ............................................................................................ +1V
Input offset adjustment ranges ...................................................... +2, +20, +200mV
Bandpass filters .................................................... 2-pole Butterworth, -12dB/octave
Low Frequency Filter ........................................................... DC, 1, 3, 10, 30, 100Hz
High Frequency Filter ........................................................... 0.1, 1, 3, 10, 30, 50kHz
Output range ..................................................................................... +10V @ 10mA
Output connector ...................................................................................... BNC jack
Stim/Record control input ......................................... TTL negative or switch closure
Data Port connector ............................................................................ 25-pin D-SUB
Dimensions .......................................................... 12W x 4H x 9D in. (31x10x23cm)
Weight .................................................................................................. 5 lbs. (2.3kg)
3.0 POWER SUPPLY CONNECTION
The POWER SUPPLY included with the BMA-400 is a universal input device that can be used
with any mains voltage in the range 95 - 240VAC, 50 or 60Hz. It is only necessary to
connect the appropriate power cord for your country. The mains cord should be plugged
into a grounded, three-wire outlet.
The output cable from the power supply is terminated with a 5-pin DIN plug. This should be
plugged into the mating connector on the rear panel of the BMA-400 mainframe.
With the power supply connected as described above, switch POWER ON via the front panel
switch. One or more indicator lights will turn on for each channel. The purpose of these
lights is described in later sections.
BMA-400 Instruction Manual 6
© 2023 CWE, Inc.
4.0 INPUTS
The INPUT connector should be wired as described below and shown in Figure 2. Note that
the maximum usable input range is about +0.5V. Higher voltages up to 50V can be
tolerated for brief periods.
Whenever possible, the differential input configuration should be used. This permits the
amplifier's common mode rejection to work by canceling noise signals present on both
active inputs. If a single-ended configuration is used, be sure to provide proper shielding of
the input leads.
4.1 INPUT CONNECTOR WIRING
For typical differential recording applications, two active leads and one common
lead are used. The two active leads are connected to pins 5 and 2 (see diagram).
Pin 3 is the COMMON connection. For single-ended applications, connect the active
lead to the (+) input pin, and jumper the (-) input pin to COMMON.
For best results, keep the input cable as short as possible, and use fully shielded
cable. The cable shield should be connected to the shell terminal of the input
connector.
NOTE! For proper amplifier operation, all three input pins MUST be
connected!
Figure 2: BMA-400 Input Connector Wiring
1
2
34
5
6
7
COMMON
+12V
-12V
-IN
+IN
BMA-400Input CablePlug
(donot usepins4or7)
BMA-400 Instruction Manual 7
© 2023 CWE, Inc.
5.0 AMPLIFIER CONTROLS
For most applications, it is only necessary to select appropriate GAIN and BANDPASS FILTER
settings. Other functions, such as stimulus passing through the recording electrodes,
require use of the DATA PORT or other connections. AC coupling is normally used for
extracellular recording and has the advantage of rejecting any small electrode voltage
imbalances which would otherwise cause difficulties. The sections below describe the
various controls available, and how and when to use them.
5.1 AC/DC COUPLING
For most extracellular recording applications, AC coupling should be used. This
permits the amplifier to ignore any small electrode potential differences that might
otherwise cause amplifier saturation. When AC coupling is selected, an effective low
frequency (high-pass) filter of 0.1Hz is inserted.
If DC amplifier response is required, set the AC/DC switch to DC, and the LOW FREQ
filter switch to DC. The variable DC OFFSET knob is activated when the AC/DC switch
is set to DC. The DC input offset can then be adjusted as required. Three adjustment
ranges are available: +2mV, +20mV, and +200mV. As shipped, the internal range
jumper is set for +20mV.
Figure 3: Front panel controls (one channel shown)
LO FREQ HI FREQ
0.1
3
10
30
50
1
CHANNEL 1
BAND-PASS
1K
2K
5K
50K
20K
10K
GAIN
500
200
20
50
100
10
DC
1
3
10
30
100
BIO
STIM
GAIN X10
ISO
DC
COUPLING
AC
OFFSET
- +
0
Hz KHz
LOW FREQ setting
(bottom knob)
HIGH FREQ setting
(top knob)
GAIN switch
DC OFFSET knob
Input coupling switch
Stimulus function active
Multiply indicated GAIN
by 10
Isolation amplifier head-
stage in use
Normal electrode
connections
BMA-400 Instruction Manual 8
© 2023 CWE, Inc.
5.2 GAIN CONTROL
The gain of the BMA-400 amplifier is set using the 12-position GAIN knob. It is
important to choose an appropriate gain setting for the input signal being amplified.
For example, if an EMG signal is known to be about 1mV P-P (peak-to-peak), and
an output signal of 1V P-P is desired, simply divide the output voltage by the input
voltage to arrive at the proper gain setting (in this case 1V / .001V = 1000). If the
gain is set too high, amplifier saturation and clipping will result. The signal-to-noise
ratio of the amplifier is best when the output is in the +1-5V range.
5.3 FILTERS
The band-pass filters contained in the BMA-400 are of the Butterworth type, for
flattest response and minimum peaking. The slope of the filters is -12dB/octave.
This sharp cutoff enables the user to select the frequency band that contains the
signal of interest. It is good practice to limit this band as much as possible, without
attenuating the desired signal. This will dramatically improve the signal-to-noise ratio
of the amplifier. Table 1 shows some typical bandpass settings for various
biopotential signals.
5.31 LOW FREQUENCY FILTER SWITCH (Outer Knob)
This switch selects the low frequency margin of the pass-band. Its range is
DC-100Hz, in 6 positions. Note that if true DC response is required, the
AC/DC switch must also be set to DC.
5.32 HIGH FREQUENCY FILTER SWITCH (Inner Knob)
This switch selects the upper frequency limit of the pass-band. Its range is
from 100Hz-50kHz, in 6 positions.
Table 1: Bandpass settings for typical applications
Application
LO FREQ
HI FREQ
EEG
0.1Hz
10 (or 100)Hz
ECG
0.1Hz
100Hz
EMG
10 (or 30)Hz
3KHz
single unit
100Hz
10 (or 50)KHz
BMA-400 Instruction Manual 9
© 2023 CWE, Inc.
5.4 INDICATOR LIGHTS
The indicator lights show important information about the configuration of each
channel. In normal operation with standard electrode connections, only the BIO light
will be lit. When head stages are in use, one or more of the other lights will indicate
special functions. These are described below:
STIM –This light indicates that the stim function is active. That is, the input leads
are temporarily disconnected from the amplifier, and connected to the
corresponding stimulus inputs (see DATA PORT).
X10 –This light indicates that the front panel gain setting should be multiplied by
ten to learn the true overall gain of the amplifier channel. When ISO-Z or
SUPER-Z head-stages are used, they will automatically telegraph their
gains to this light.
ISO –This light indicates that an isolation amplifier head-stage is in use.
BIO –This is the default indicator light. It indicates that standard, non-isolated
inputs are in use.
6.0 OUTPUT (Rear Panel)
The amplified output signal for each channel is obtained from the corresponding OUTPUT
BNC jack on the rear panel. This signal may be directly connected to most recording or
monitoring devices, providing that their input impedance is 1000 ohms or greater. For best
performance, use a shielded coaxial cable to connect the OUTPUT to your recording device.
The output is short-circuit protected, but the output circuits can be damaged if a voltage is
connected to this jack. The channel output signals are also available on the DATA PORT
connector.
7.0 STIM/RECORD FUNCTION
The STIM/RECORD function allows the user to pass stimulating currents to the recording
electrodes. When this function is active, the internal amplifier inputs are disconnected, and
the (+) and (-) input connector pins are routed to the rear panel STIMULUS INPUT
CONNECTIONS (see DATA PORT).
While this function is most often used for passing a stimulus to the recording site, it can also
be used an input blanker. For example, if the recording electrodes are frequently
repositioned, using this function will prevent amplifier saturation while the recording
electrodes are moved.
The STIM/RECORD CONTROL input (see DATA PORT) accepts TTL negative logic signals, or
can simply be activated with a switch closure between the control pin and ground. A
footswitch wired for this purpose is convenient for input blanking. This function operates via
a reed relay. Response time is approximately 2.5mS.
BMA-400 Instruction Manual 10
© 2023 CWE, Inc.
8.0 DATA PORT CONNECTOR (REAR PANEL)
The DATA PORT connector on the rear panel provides access to the following functions:
stimulus inputs (two per channel); stimulus control inputs (one per channel), and; additional
output signals (one per channel). The required connector is a standard 25-pin D-SUB male
plug. Figure 3 shows how these functions are accessed from the DATA PORT connector.
STIMULUS INPUTS –These inputs provide a means of temporarily connecting an external
stimulus to the recording electrodes. When the STIMULUS function is active, the (+)
and (-) stimulus inputs are connected to the corresponding input leads.
STIMULUS CONTROL INPUT –This input activates the STIMULUS function. The required
signal is a logic low (approx. 0 - 0.4V). A simple switch closure to ground will also
activate this function.
OUTPUT SIGNALS –These pins provide an additional means of accessing the individual
amplifier output signals. They are identical to the signals present on the regular
OUTPUT jacks.
DATA PORT
Required connector is
DB25P male plug
Figure 4: DATA PORT connections
BMA-400 Instruction Manual 11
© 2023 CWE, Inc.
9.0 SETTING THE DC OFFSET RANGE
The range of the front-panel DC OFFSET control can be set to one of three ranges: +2mV,
+20mV, or +200mV. This is accomplished by placement of an internal jumper on the circuit
board. The following procedure describes how the jumper is set.
Remove the top cover of the case to expose the circuit boards.
Locate the OFFSET RANGE jumper block near the top center of the circuit board.
Place the jumper across the appropriate pair of terminals using the silk-screened
legend as a guide.
Replace the top cover. The range of the DC OFFSET control will now match the jumper
setting.
10.0 OPTIONAL HEAD-STAGES
For special applications, the BMA-400 can be used with optional head-stages. Positive and
negative supply voltages are present on the input connector for the purpose of powering
external devices. For human subject recording requiring absolute patient safety, you should
use the ISO-Z Isolation Amplifier head-stage. This device guarantees that no current will
flow to the subject, and complies with UL-544 safe current limits. For very high-impedance
microelectrode use, the SUPER-Z High-Impedance Head-stage is available. This accessory
preamplifier/buffer uses matched high-impedance buffers compatible with any electrode
type, including ion-specific microelectrodes. In addition, the SUPER-Z includes switchable
10X gain, allowing an overall amplifier gain of 500,000X. All the accessory head-stages use
standard 2mm (0.080") diameter pin jacks as input connectors, except the ISO-Z, which
uses the required 1.5mm DIN safety socket connections.
11.0 USING TRANSDUCERS WITH THE BMA-400
The BMA-400 has its supply voltages present on the input connector. The primary purpose
of this feature is to power the optional head-stages described earlier. These voltages are
+12V. With care, it is possible to use these voltages as bridge excitation for pressure, force,
or acceleration transducers. A simple voltage regulator circuit can reduce the voltages to,
say, +5V if required. Since there is no current limiting provided, care must be exercised not
to draw too much current from this source. A practical maximum would be about 25mA.
Contact CWE if you are interested in designing or building such a device.
BMA-400 Instruction Manual 12
© 2023 CWE, Inc.
12.0 ORDERING INFORMATION
PART NO.
MODEL
DESCRIPTION
09-03010
BMA-400
Four-channel AC/DC Bioamplifier, with international power supply and four
input cables (order electrode leads separately)
09-04000
ISO-Z
Isolation Amplifier Head-Stage, 1.5mm safety socket connections
10-02030
HS-1
High-Impedance 1X Head-Stage, 2mm pin jack connections
09-03112
ICA-400
Pre-wired input cable, 9' (2.7m), with 1.5mm safety sockets
10-02040
BMA-931/CON
Spare unwired input connector
10-02064
D-482
Disposable pre-gelled ECG-type electrode, snap connect, pk of 300
10-02063
E-422
Snap-type electrode lead, 39" (1m) long, 1.5mm safety plug, pk of 3
10-02064
NEE-3
Needle electrode lead, 1.5mm safety plug, pk of 3
10-02065
Alligator Lead
Alligator clip electrode lead, 1m long, color-coded, set of 3
10-10010
BNC-3
BNC-BNC patch cable, 3’ long
10-10011
BNC-6
BNC-BNC patch cable, 6’ long
10-10012
BNC-20
BNC-BNC patch cable, 20’ long
10-02050
PIN-PLUGS
Set of 3 color-coded miniature pin plugs for custom cables, unwired
10-02051
PIN-DIN Adapter
2mm pin jack to 1.5mm DIN safety-socket plug, 5” (13cm) long (allows use
of PIN-PLUGS with ICA-400 cable and ISO-Z head-stage, set of 3
09-03200
BMA-400 PS
110/220V international power supply
09-03011
RACK-MOUNT
Rack-mounting kit for BMA-400
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