CAMBRIDGE CED 1902 User guide

i
The CED 1902 Mk IV Owners Handbook
Copyright Cambridge Electronic Design Limited 2017
Neither the whole nor any part of the information contained in,
or the product described in, this guide may be adapted or
reproduced in any material form except with the prior written
approval of Cambridge Electronic Design Limited.
1st edition (1.0) October 1991
2nd edition (1.5) February 1992
3rd edition (2.0) March 1997
4th edition (2.1) September 1997
5th edition (3.0) May 2006
6th edition (3.1) May 2008
7th edition (3.2) July 2012
8th edition (3.3) August 2014
9th edition (3.4) May 2017
Published by:
Cambridge Electronic Design Limited
Technical Centre
139 Cambridge Road
Milton
Cambridge
CB24 6AZ
UK
Telephone: [phone]
USA & Canada Toll Free 1-800-345-7794
Web: www.ced.co.uk
Email: [e-mail]
Trademarks and Tradenames used in this guide are
acknowledged to be the Trademarks and Tradenames of their
respective Companies and Corporations.

Table of Contents
ii
Publishing information.................................................................i
Table of contents........................................................................ ii
Life support.................................................................................v
Potential for Radio/Television Interference (USA only)............v
Storage and operating environment...........................................vi
Protection...................................................................................vi
Typographic conventions......................................................... vii
Use of symbols......................................................................... vii
Introduction.................................................................................1
Checklist......................................................................................1
The Electrode Box ......................................................................2
The Active Head Stage ...............................................................3
Installing the 1902 software........................................................5
Confidence check – Try1902......................................................5
Machine control ..........................................................................7
Electrical isolation.......................................................................7
RFI approvals....................................................................7
Safety approvals................................................................7
Signal input to the 1902..............................................................8
1902 functional organization ....................................................10
The waveform conditioner..............................................10
The trigger generator......................................................10
Features seen by the user ..........................................................12
Preface
Installation
General
information

Table of Contents
iii
Physical construction................................................................13
Installations with multiple 1902s...................................13
Rack mount installations................................................13
Using a USB port .....................................................................13
Channel numbers and how to set them.....................................14
1902 communication configuration .........................................14
Cable connections.....................................................................16
Power..............................................................................16
RS232.............................................................................16
Signal cables...................................................................16
Electrode cables .............................................................17
Mating connectors....................................................................17
Firmware – the 1902 flash ROM..............................................18
Software supplied with the 1902.............................................. 20
The Stand-alone Control Panel ................................................20
The control panel with CED applications................................ 22
Running the 1902 from Spike2.................................................23
Running the 1902 from Signal.................................................24
Main amplifier..........................................................................25
Isolation pre-amplifier..............................................................26
Isolated input............................................................................27
Transducer input.......................................................................28
Bridge transducers..........................................................29
Single-ended transducers ............................................... 29
Trigger circuit...........................................................................30
Wiring switches..............................................................31
RS232 cable.............................................................................. 32
Power supply............................................................................33
The hardware
Application
software
Electrical
Specification

Table of contents
iv
Basic mode of operation ...........................................................34
Multiple independent channels.................................................35
Multi-channel configurations and the1902 input buffer...........36
1902 input clamp option ...........................................................41
Use of the notch filter ...............................................................43
Theory of electrical isolation....................................................44
Cleaning the 1902 .....................................................................46
Updating firmware....................................................................46
Calibration.................................................................................46
Opening the 1902......................................................................47
Try1902: the calibration utility.................................................48
Contacting CED........................................................................49
Servicing the 1902 ....................................................................50
The 1902 motherboard..............................................................51
Features of the motherboard .....................................................52
Circuit diagrams........................................................................52
Exchanging 1902 daughterboards.............................................53
Updating the EEPROM.............................................................54
The EEG daughterboard ...........................................................55
The ECG daughterboard ...........................................................56
The filter daughterboard ...........................................................57
Index..........................................................................................58
Important note...........................................................................61
EC Declaration of Conformity..................................................62
Details of
operation
Inside the 1902
Index
EC Declaration
of Conformity

Preface
v
CED products are not authorized for use as critical
components in life support systems without the
express written approval of the chairman of the board
of directors of CED.
Life support systems in this context are systems which support
or sustain life, and whose failure to perform, when properly
used in accordance with instructions for use provided, can be
reasonably expected to result in a significant injury to the user.
A critical component in this context is any component of a life
support system whose failure to perform can reasonably be
expected to cause the failure of the life support system, or to
affect its safety or effectiveness.
The 1902 generates and uses radio frequency energy and may
cause interference to radio and television reception. Your 1902
complies with the Specification in Subpart J of Part 15 of the
Federal Communications Commission rules for a Class B
computing device. These specifications provide reasonable
protection against such interference in a residential installation.
However there is no guarantee that interference will not occur
in a particular installation. If the 1902 does cause interference
to radio or television reception, which can be determined by
turning the 1902 off and on, you can try to eliminate the
interference problem by doing one or more of the following:
•Re-orient the receiving antenna
•Re-orient the position of the 1902 with respect to the
receiver
•Move the 1902 away from the receiver
•Plug the 1902 into a different outlet so that the 1902 and the
receiver are on different branch circuits
If necessary, consult CED or an experienced radio/television
technician for additional suggestions. You may find the
booklet, prepared by the Federal Communications Commission,
helpful: How to Identify and resolve Radio/TV Interference
Problems. This is available from the US Government Printing
Office, Washington DC 20402, Stock no. 004-000-00345-4.
To comply with FCC rules, Part 15 J Class B Computing
device, use only shielded interface cables.
Life support
Potential for
Radio/Television
Interference
(USA only)

Preface
vi
The storage and operating environment for a 1902 must not
exceed the temperature range 0°to +50°Celsius, in conditions
of non-condensing humidity which should not exceed 95%
saturation, in an atmospheric pressure range of 500 hPa to
1060 hPa. The 1902 complies with relevant EU and USA
requirements for electromagnetic interference. The 1902 is
suitable for continuous operation. The 1902 is not protected
against ingress of water or dust. There are no hazardous
voltages inside the 1902. The 1902 can be recycled; please
contact CED for further details.
The 1902 offers Class I protection against electric shock. To
maintain the safety standard, accessory equipment attached to
the 1902 must also comply with relevant safety requirements
such as IEC601-1 or the relevant IEC standard e.g. EN60601-1
configured to comply with EN60601-1-1:2000.
The ‘Common’ lead on a three-wire electrode cable provides a
return path for the input amplifier bias currents. UNDER NO
CIRCUMSTANCES should this lead or any other electrode
lead be connected to mains earth. This will negate the 1902’s
isolation provisions and expose subjects to the risk of fatal
shock.
The 1902 is not protected against flammable anaesthetic
mixtures. It must NOT be used in the presence of such
mixtures.
Storage and
operating
environment
Protection
Electrode
‘Common’ leads
Anaesthetic gases

Preface
vii
The following conventions apply to the text in this manual:
•Titles of manual sections, other manuals and other
publications are in italics
•Labels and identifiers appearing on the equipment described
in this manual are in Arial
•Menu items, buttons, and other contents of computer displays
are in Arial italics
•Text entered by keyboard is in Courier New. Names of
keys are enclosed in angular brackets, e.g. <esc>, <enter>
Where applied, the symbols below have the following
meanings:
This symbol is used on the CED-approved power supply, to
denote that the electrical isolation is to IEC Type B standard.
This symbol is used on the power supply to indicate the mains
input is for AC power only.
This symbol is used on the power supply to show that the
outputs are DC only.
The CED 1902 is subject to the EU WEEE regulations and may
be returned to CED Ltd. for recycling.
Observe precautions against electrostatic discharge.
Attention, consult accompanying documents.
Typographic
conventions
Use of symbols

Installation
1
This section will guide you through the installation of your
CED 1902 Mk IV isolated pre-amplifier. This involves loading
the operating software and running an initial confidence check.
The installation kit for your 1902 comprises:
•One or more 1902s, either free-standing or rack-mount
•A power block with attached DC power cable
•A power-block mains cable suitable for your country
•An RS232 cable to connect the 1902 to your computer
•A kit of accessories, including plugs to match the front-
panel connectors
•An installation disk to allow you to install and check out
your 1902
•CED Electrode or Head Stage Boxes (optional)
•This owners manual
The 1902 power block will run with no adjustment on any
mains voltage from 100 V to 240 V, 50 Hz - 60 Hz, drawing
1.3 A maximum. It has no switch, being controlled by plugging
in and switching on at the mains socket.
The 1902 itself has no DC
power switch. For
electrical isolation to be
complete, mains power
must be disconnected from
the power block.
Use only the cables
supplied by CED. They
have the metal shells and
screening braid that are
necessary to meet the
requirements for control of
electromagnetic inter-
ference. Others may not do
so.
Introduction
Checklist
The power block
The power block
Powerbox™ PMP55 shown
Cables

Installation
2
The CED1902-11 family comprises optional electrode adaptor
boxes that plug into the electrode input sockets of CED 1902
isolation amplifiers. There are four variants of the smaller box:
•CED1902-11-2 2 channel (bipolar)
•CED1902-11-2B 2 channel (bipolar or common-reference)
•CED1902-11-4 4 channel (bipolar)
•CED1902-11-4B 4 channel (bipolar or common-reference)
CED also manufactures two 16-channel electrode boxes:
•CED1902-11-16 16 channel (common-reference)
•CED1902-11-16B 16 channel (bipolar or common-reference)
The electrode boxes have
input connectors for up to
16 electrode pairs plus
common electrodes. The
connectors can be either
1.5mm or 2mm safety
(touch-proof) types. The
boxes are passive, i.e. they
do not amplify the signals.
The outputs are connected
to the electrode inputs of
CED 1902 isolation
amplifiers via shielded
cables. The boxes have two
or more Common input
connectors that are linked
together and to the
Common leads of all the
output cables. The interior
of the box is coated with
electro-conductive paint
which is electrically
connected to the screens of
the output cables.
The Electrode Box
The 1902 Electrode Box
2-channel model shown

Installation
3
The –B option on the 2- and 4-channel boxes adds an input and
output connector for the 1902 buffer option and also a rotary
switch for selecting common-reference (buffer output drives all
the –ve inputs) or bipolar (buffer not used) modes of operation.
Note that the buffer connectors are inoperative unless the
correct output lead (usually channel 0) is connected to a
CED 1902 fitted with the buffer option. For details of common-
reference operation using a buffer, see page 36.
The 16-channel boxes are available with either 16 signal
electrode inputs plus common reference or 16 electrode pairs
plus 4 buffer connections.
The CED1902-10 Active Head Stage is an optional electrode
adaptor box similar to the CED 1902 11 mentioned above, with
safety-plug connections for up to four electrodes. It contains
either two or four channels
of battery-powered differ-
ential amplifiers with
switchable gains of ×1, ×3,
and ×10. The outputs are
AC coupled, with a corner
frequency of 1.6 Hz. The
Active Head Stage links
together the Common leads
of all electrodes connected
to it. The 1902 clamp
option (see page 41) cannot
be used if this adaptor is
present, because its
amplifiers are upstream of
the clamp circuitry. If
clamping is required, the
CED 2804 External Clamp
Box should be considered
instead.
Buffer option
The Active Head
Stage
The 1902 Active Head Stage
4-channel model shown

Installation
4
This four-channel device can be used with any amplifier to
prevent input saturation, as for instance when high voltages or
intense magnetic fields are used as stimuli. On receipt of a TTL
signal from external
trigger equipment it
clamps incoming
electrode signals for
the duration of the
trigger signal. It can
operate in several
different clamping
modes, as selected by
a rear-panel switch.
The External Clamp
Box
The 2804 External Clamp Box

Installation
5
To install the 1902 operating software, autorun the 1902
Support CDROM supplied with the hardware. This should be
completely automatic under any version of Windows. It will
install Try1902, a diagnostic and calibration program. It will
also install the 1902 Control Panel, which can be opened by the
user to run the 1902 in stand-alone mode.
Once the software is installed, you can run Try1902 to check
that the 1902 is, to the first order, working, and has not been
damaged in transit. Before it is run, the 1902 must be powered
up and connected to your computer.
With mains power off, insert the DC power cable and the
RS232 cable into the back of the 1902. The power cable will
only plug-in one way, and the RS232 cable is reversible end-
for-end. Make a note of which physical com port the RS232
goes into (most likely Com1; many computers only have one
com port.) Some computers, especially laptops, have no com
port at all; in this case, use a USB–RS232 adaptor (see
page 13).
Switch 1902 power on at the mains. Observe on the front panel
that the green Power LED comes on. Open Try1902 by
selecting Start, Programs, 1902 Support, Try1902.
First of all, you must set the com port and the 1902 channel
dropdown lists. These identify the com port being used, and the
channel number to which the 1902 is set. As soon as they
correspond to the 1902 present, it will be identified and
reported. In multiple installations, where all 1902s share the
same com port, the 1902 identified will change as the channel
number is changed. The numbers will correspond to the 1902
unit numbers (0, 1, 2, etc.) In single installations the channel
number will be 0, unless specified otherwise.
This is the most basic test, simply checking that the 1902 will
accept and return data. Press Communications test to start the
test; Stop testing stops the test and reports the number of passes
(repetitions) done, and errors found, if any.
Installing the
1902 software
Confidence
check – Try1902
Connecting the
1902
Running Try1902
Com port and
channel number
Communications
test

Installation
6
Try1902 with Trigger test prompt
Pressing Trigger test opens a small window that invites you to
test the trigger inputs with a signal generator and oscilloscope.
However, just toggling the two radio buttons will change which
of the yellow Gate LEDs is lit on the front panel.
EEPROM test checks the validity of data in a part of the flash
ROM that is equivalent to the EEPROM of earlier 1902s. This
stores information that is specific to the 1902 in question, such
as its serial number and daughterboard configuration. The test
takes a few seconds, and reports either success or failure.
If you are familiar with the 1902 command set (documented in
the 1902 Technical Manual), you can send command strings to
the 1902 by selecting Interactive mode. Vary parameters
allows you to set the high- and low-pass filters, the notch filter,
and AC coupling, as well as input mode, gain and offset.
Calibrate amplifiers opens the calibration procedure; this is
dealt with below (see page 46.)
Trigger test
EEPROM test
Other tests

General information
7
In equipment used in research and industry, it is highly
desirable that all functions of instrumentation are readable and
controllable by computer. The 1902 achieves this by one of the
most universal means: the RS232 serial line, or else an RS232
virtual port implemented on a USB adaptor.
When recording electrophysiological signals from live human
subjects, it is a legal and ethical necessity to protect them from
electric shock. This is all the more so since, with electrodes
close to vital organs, a very small current can be fatal.
Consequently, the 1902 has provision for an isolation amplifier
that has been approved for use with human subjects.
The 1902 has been type-tested and found to meet the
requirements of the European EN55022:1987 Class B and the
USA FCC Part 15 J Class B radio frequency interference
specifications when used with the specified power supplies and
cables.
The 1902 meets the safety requirements of BS EN5724
(IEC EN60601-1) when used with a CED-approved power
supply, BSI certificate no 221/000018, issued 17 September
1997.
The 1902’s isolation approvals may not be relevant to industrial
users. The unit will run on other power supplies (see page 32)
but it is important to note that the 1902 does not meet
EN 60601-1-1:2000 safety and EN 60601-1-2:2001 EMC
standards unless used with the CED-approved power supplies.
Machine control
Electrical
isolation
RFI approvals
Safety approvals
Warning

General information
8
To amplify signals with
the 1902, you must first
select the input source
and mode of operation.
The sources are the
transducer and the
isolated amplifier. You
cannot use both at once.
The transducer has four
input modes; the isolated
amplifier operates either
normally, i.e. with
differential inputs, or
with a clamp of varying
duration. The source and
mode are selected by one
drop-down list in the
1902 Control Panel. See
page 20 for how to open the Control Panel, and for more about
the other controls. See page 41 for a description of input
clamping.
Please note that the input source DEFAULTS TO THE
TRANSDUCER.
If you wish to use EEG (or ECG, EMG, etc.) input, you must
first SELECT ONE OF THE ISOLATED INPUTS mentioned
above.
Signal input to
the 1902
Input drop-down list;
version with electrode clamping
Important!

General information
9
The input modes are tabulated below. For the pinout of the
transducer and isolation amplifier sockets, see pages 27 and 28.
For more on the fundamentals of differential input, see page 34.
Note that, when selecting isolated input, ‘EEG’ is taken to
include ECG, EMG, etc.
Source
Mode
Effect
Transducer
Grounded Both amplifier inputs grounded
Single ended Input +ve to amplifier non-inverting
input; inverting input grounded
Normal diff. Input +ve to non-inverting input;
Input –ve to inverting input
Inverted diff. Input +ve to inverting input;
Input –ve to non-inverting input
Isolation
amplifier
Grounded EEG Both amplifier inputs grounded
Isolated EEG /
EEG unclamped Input +ve to non-inverting input; Input –ve to inverting input
Clamped EEG —
0.5 ms, 1.0 ms, … 12 ms,
14 ms
Differential input as with normal EEG,
but input is clamped (see page 41) for
interval selected
Input mode table

General information
10
To the user, the 1902 comprises two completely separate
functional blocks: the waveform signal conditioner and the
trigger generator.
The waveform conditioner provides one channel of output, with
the input selected via software from a range of input
connections. There is a comprehensive set of conditioning
controls: gain selection, filtering and offsetting, and overrange
detection. The 1902 may readily be adapted to different
specialized signal sources, requiring additional control (for
instance clamping), by a choice of internal daughterboards. The
computer can read back the characteristics of these daughter-
boards.
By default, digital filtering is installed in your 1902 (the
alternative being analogue filter sections on a daughterboard).
The digital filter processing section is based on a 16-bit ADC
carrying out conversions at 30 kHz; this interrupts the
microprocessor, which carries out digital processing as required
before writing the modified data to the DAC, which is also
clocked at 30 kHz. The digital processing imposes a time delay
(latency) of approximately 0.35 ms on the data at the time of
recording. During playback, Spike2 or Signalcan be configured
to remove this delay if required.
2-pole or 3-pole digital filters can be applied, with either Bessel
or Butterworth response. The corner frequencies are selected
from dropdown lists, or users may type in their own values:
high-pass from 0.01 to 1000 Hz, low-pass from 1 to 10,000 Hz.
There is a rectification option, useful for EMG studies. The
digital filtering system can also be used to output ADC data
down the serial line at up to 100 Hz.
The trigger generator provides one output channel of pulses,
derived from a choice of two inputs selected by program. It
uses comparator circuitry with hysteresis to generate clean TTL
pulses from a variety of trigger input sources.
The Trigger2 input can be used to trigger the EEG input-
clamping circuit, if this option has been fitted (see page 41).
1902 functional
organization
The waveform
conditioner
Digital filter
Response
The trigger
generator

General information
11
Waveform signal flow in the 1902,
detailing digital filtering subsystem

General information
12
Features of the 1902, all selected by program control, are:
•Differential or single-ended transducer waveform inputs
(non-isolated, not for human subjects)
•Optional isolated EEG electrode input
•Optional input clamping with EEG input
•Optional isolated ECG 5-lead input selection
•Gains from ×100 to ×100,000 in steps of ×1, ×3, ×10…
•Optional gains from ×1,000 to ×1,000,000 in steps of
×1, ×3, ×10… (build option)
•AC/DC coupling switch
•12-bit DC voltage offset
•Selectable mains-frequency notch filter, 50 Hz or 60 Hz
•Overload indicators, readable by computer
•Trigger input: converts from high-level pulses or switch-
closures to TTL, with program-selectable choice of 2 inputs
(non-isolated)
•Digital filter with a wide range of user-selectable settings
•Optional precision unity-gain buffer for use in multi-
electrode configurations
Features seen
by the user