MODEL 401 TCP/IP-INTERFACED
                             24-BIT DATA ACQUISITION SYSTEM

                                                     LAWSON LABS, INC.
                                                     3217 Phoenixville Pike
                                                     Malvern, PA  19355

                                                        610 725-8800
                                                             or
                                                        800 321-5355

                                                   e-mail lawsnlab@netaxs.com
                                                   web    www.lawsonlabs.com
             Rev. A

                                    TABLE OF CONTENTS

             INTRODUCTION                                                  1

             SECTION 1: INSTALLATION                                       2

             SECTION 2: OPERATION                                          3
                 Establishing Communications                               3
                 Polled Mode Overview                                      4
                 Software Calibration                                      4
                 Connecting Analog Inputs                                  4
                 Connector Pinout                                          5
                 Digital Input/Output                                      5
                 Other Commands                                            6
                 Scanning Mode                                             6

             SECTION 3: OPERATING SUGGESTIONS                              7

             SECTION 4: TROUBLESHOOTING                                    8

             SECTION 5: INTERNAL ADJUSTMENTS                               9

             SECTION 6: MODEL 401 SPECIFICATIONS                          10

             WARRANTY                                                     11

                                                                         page 1
                                      INTRODUCTION

                 The Lawson Labs, Inc. Model 401 24-Bit Data Acquisition
             System is a high-resolution device for translating voltages
             into digital form. The Model 401 communicates with a host
             computer using the TCP/IP protocol over a 10Base-T link. It
             has two multiplexed differential analog input channels and eight
             each digital input and digital output lines. The analog input
             and digital I/O sections are electrically isolated from the
             computer.

                 The Model 401 is intended for DC and low frequency
             applications. The data rate is programmable from 10 to
             1000 samples/second. At a data rate of 10 samples/second,
             the RMS noise approaches one count, providing 23 bits
             effective resolution. (The converter is guaranteed monotonic
             to 23 bits.) Effective resolution decreases with increasing
             data rates. Even so, 20-bit effective resolution is maintained
             at 1000 samples/second.
                 The Model 401 requires a single DC supply in the range of
             15 to 30 volts to power the isolated circuitry.Current draw is
             typically 115 milliamps in normal operation. The power and analog
             inputs are protected against substantial overvoltages.
                 Both polled and scanning modes are available. In scanning
             mode, the Model 401 maintains its own time base and transmits
             a pre-defined scan of one or two input channels at a preset
             interval. Self-calibration can remove offset and gain errors
             under software control.
                 The exceptional resolution, stability, flexibility and
             price are achieved by combining an accurate, but complex,
             delta-sigma type A/D converter with a microcontroller
             supervisor. The microcontroller simplifies the task of
             interfacing to the converter itself.

                                                                         page 2
             SECTION 1: INSTALLATION

                 The Model 401 interconnections consist of a DB25 connector,
             for input and output, an RJ45 connector for TCP/IP, and a 2-
             terminal power connector. Use a crossover cable if the Model 401
             connects directly to the PC or server. Use a standard cable if it
             connects to a hub.

             NOTE:  Always handle circuit cards by the edges. Static
                    electricity can damage computer circuitry, so care
                    should be taken to control static discharge.

                 For operational checks, only the power supply and TCP/IP
             cable need be connected. The power supply voltage can range
             from 14 to 28 VDC and does not need to be regulated. Power
             is connected to the terminals on the orange terminal block.
             The power terminals are labeled "+" and "-". The wall-mounted
             transformer supplied has a white stripe on the positive wire.
             Any regulated or unregulated power supply with high enough
             current ratings (within the correct voltage range) can be
             substituted. The board is protected against reverse voltage but
             will not operate without a properly connected supply. The power
             can be connected before or after the interface connection is made.

             Note that the computer chassis ground is not connected to ground
             at the Model 401 because of the isolation. If your Model
             401 has been mounted in the standard enclosure it will have a 47K
             ohm resistor placed between the computer's ground and the Model
             401's chassis ground. This resistor should be removed if the two
             grounds are to be more than 100 volts apart. (Contact the factory
             for details.)

                 For maximum accuracy the board should be enclosed in a
             shielded box. Open cell foam is placed against both sides of the
             board to minimize air currents. Although a copper/solder junction
             is not considered a good thermocouple, there are many such
             junctions and collectively, they can have an effect on the least
             significant bits.

                                                                         page 3
             FIGURE 1: MODEL 401 BLOCK DIAGRAM

             

                 The software drivers provided include a DLL and sample
             application code, with source, in VC or VB. Win98, 2K & XP are
             supported. Refer to the read_1st.txt file on the disk before
             installing the software. The latest version of the driver software
             and sample application code can be downloaded at no charge from
             www.lawsonlabs.com.

             SECTION 2: OPERATION

             Establishing Communications

                 Once the software is installed, run the executable version of
             the VC or VB sample application. You will need VB installed on the
             PC in order to run the VB code supplied. Before any other
             communications can succeed, the Model 401 needs to be initialized.
             Each Model 401 has a unique mac identification number permanently
             programmed into the controller and printed on its label. If your
             server uses dynamic IP address assignment, you may need to enter
             the mac number in a configuration table before the server will
             recognize the Model 401. Follow the software start-up instructions
             carefully when connecting the Model 401 to your network. See the

                                                                         page 4

             Troubleshooting section of this Manual if you have difficulty
             connecting.

             The Model 401, when first connected to the network will attempt to
             get an IP address assigned via BOOTP or DHCP. If that doesn't
             succeed before the programmable timeout expires, the last saved IP
             address stored in non-volatile memory will be used. Both the time-
             out and the default IP address can be changed from the
             configuration menu.

             Polled Mode Overview

                 In polled mode, individual conversions are requested with
             individual commands. Other commands set the digital outputs,
             change input channels, recalibrate the system, or change to
             scanning mode. To maintain compatibility with earlier
             products, the offset correction channel is designated channel 7.
             The full scale calibration channel is designated as
             channel 6. The two available analog input channels are called
             channels 0 and 1.

             System Calibration

                 To confirm proper operation, select channel 7 and you should
             see a voltage very close to zero. The offset portion of the system
             calibration removes errors caused by the input signal conditioning
             circuitry as well as offset errors in the A/D converter itself.
             Confirm that the reading is close to zero volts. Channel 6 should
             read close to +5 volts (or other full scale value) after a system
             calibration. The full-scale calibration removes gain and signal
             conditioning errors.

             Connecting Analog Inputs

                 A battery is a convenient voltage source for checking the
             Model 401. Connect the positive and negative ends of the battery
             to a pair of positive and negative analog input pins on the analog
             input connector. (Pins 14 and 1, respectively for channel 0). You
             will also need a wire from one end (normally the negative) of the
             battery to ground at the Model 401 to insure that the input
             voltage at both input terminals is within 6.5 volts of ground. The
             ground at pin 3 is provided for the purpose. This extra ground is
             for common-mode requirements only, and, while necessary, it is
             non-critical. Remember that the Model 401 is electrically isolated
             and floats in relation to the computer chassis ground. A typical D
             cell should read about 1.5 volts. Reverse the wires and note the
             polarity change. Connecting the input wires directly together will
             cause a potential of zero volts. An open circuit will read
             unpredictably. A positive overvoltage will read 5 volts. A
             negative overvoltage will read -5 volts. The analog input channels
             are protected against continuous overvoltage up to 60 volts.

                                                                         page 5

                 Because of the extreme resolution possible with the Model 401
             it is necessary to carefully shield your input signals from
             electrical noise. Electrical noise can be radiated through the
             air and picked up by wiring and/or circuitry. It can also be
             introduced via the power connections. Also, air currents can
             create sufficient temperature changes to cause thermal noise.

             FIGURE 2: 25-PIN CONNECTOR PINOUT

                        PIN 13..Digital Ground
                                                 PIN 25..Digital Out 7
                        PIN 12..Digital In 0
                                                 PIN 24..Digital Out 6
                        PIN 11..Digital In 1
                                                 PIN 23..Digital Out 5
                        PIN 10..Digital In 2
                                                 PIN 22..Digital Out 4
                        PIN 9...Digital In 3
                                                 PIN 21..Digital Out 3
                        PIN 8...Digital In 4
                                                 PIN 20..Digital Out 2
                        PIN 7...Digital In 5
                                                 PIN 19..Digital Out 1
                        PIN 6...Digital In 6
                                                 PIN 18..Digital Out 0
                        PIN 5...Digital In 7
                                                 PIN 17..Digital Ground
                        PIN 4...Digital Ground
                                                 PIN 16..Analog Ground
                        PIN 3...Analog Ground
                                                 PIN 15..CHANNEL 1+
                        PIN 2...CHANNEL 1-
                                                 PIN 14..CHANNEL 0+
                        PIN 1...CHANNEL 0-

             Note:  For maximum protection, any unused input terminals
                    should be connected to ground. This is done to protect
                    the circuitry from static discharges which can be of
                    extremely high voltage. Open inputs can also pick up
                    noise. Strain-relief is recommended for all permanent
                    wiring on the connector. Otherwise, physical stress may
                    cause the failure of an electrical connection.

             * Pin 13 can, optionally, serve as a trigger input.

             Digital Input/Output

                 The digital input word, from pins 5 through 12 on the
             input/output connector, is updated with each conversion
             in polled mode and with each packet of ten conversions in
             normal scanning mode. For digital input scanning, the digital

                                                                         page 6

             input byte is updated and transmitted once per conversion. The
             digital inputs are active low. They can be activated by a contact
             closure to digital ground or by any 5 volt logic signal referenced
             to the same ground.The digital input word is displayed as an
             integer between 0 and 255. You may want to view it in binary
             format so that individual inputs show as ones and zeros.
                 The digital output command puts a latched 8-bit digital word
             at pins 18 through 25 on the input/output connector. Valid values
             are in the range of 0 to 255. The digital outputs are buffered to
             source or sink 20 MA. Note that when sinking current, the voltage
             may rise significantly above 0 volts.

             Other Commands

                 The A/D converts constantly at the selected rate. That rate
             determines the frequency response of the converter. Rates from
             10 to 1000 Hz are supported. There is a low-pass filter intrinsic
             to the conversion process. The cut-off frequency of that filter
             is the data rate times 0.262. For maximum effective resolution
             use the lowest data rate that meets your needs. For rates lower
             than 10 Hz, average in the application, or discard the extra data.
             Note that 1 / rate must be an integer multiple of the A/D's
             clock period. Therefore, the actual rate selected and displayed
             may be slightly different than the rate you enter.

                 The application can keep a running average of N consecutive
             conversions. The Model 401 is specified with the running
             average set to four.

             Scanning Mode

                 The Model 401 will send data back continuously at the preset
             rate once a start scan command is sent. There are three different
             types of scan, single-channel with digital input, multi-channel
             with digital input, and multi-channel with digital input and
             calibration data. For single-channel scanning, the Model 401 will
             take data on whatever channel was selected when the scan was
             started. Channel change commands can be sent at any time during
             single-channel scanning. For multi-channel scanning, the Model 401
             controls the channel selection. Do not send channel change
             commands during multi-channel scanning. You can send digital
             output commands at any time during any type of scan without
             altering the data acquisition timing.

                 Calibration scan adds a reading of channel 7, the offset
             channel, at the end of each scan. The software then subtracts
             the offset value from the other data to provide active zero-drift
             suppression.

                                                                         page 7

             SECTION 4: OPERATING SUGGESTIONS

                  The Model 401 features fully differential inputs. A basic
             understanding of differential measurements will help you to use
             your card to best advantage. The plus and minus input pins should
             be wired directly to the voltage being measured. In this way, it
             is assured that the only current flowing in the wires will be the
             input current of the A/D converter. Because the wires have finite
             resistance, any current flowing will cause a voltage drop and a
             corresponding error. The Model 401 requires a vanishingly small
             input current so the error caused by even very long wires is
             negligible. For proper operation it is necessary that the positive
             and negative inputs both be within 6 volts of ground. For a
             floating voltage source, this is generally accomplished by
             connecting a third wire between the Model 401 ground and a ground
             terminal at the source of the measured voltage. Ground currents
             may flow in this wire, but the resulting voltage drop will not
             cause a measurement error. Redundant grounding can cause ground
             loops. Ground loops can cause erratic behavior because currents
             will flow through different paths at different times causing
             unpredictable voltage drops.

             FIGURE 3: TYPICAL INPUT CONNECTIONS

             * Remember to ground unused inputs

             Best results are obtained with filtered, buffered voltages.
             Electrical noise travels through the air and can be picked up
             by interconnecting wires. The first defense against noise is
             shielding. Use shielded wire with the shield connected at one
             or both ends to ground. (See above.) The lower the impedance
             of the voltage source, the less susceptible the wiring will be
             to electrical noise. If noise problems persist, try to locate

                                                                         page 8

             the source of the interference and shield it. Electric motors,
             electric heaters and flickering fluorescent lights are potential
             sources of interference.

              FIGURE 4:  EFFECT OF DATA RATE ON EFFECTIVE RESOLUTION
                          AND SETTLING TIME

             DATA RATE      EFFECTIVE RESOLUTION       SETTLING TIME

              10 Hz                   23                   800 MS
              50 Hz                   22.5                 160 MS
             100 Hz                   22                    80 MS
             250 Hz                   21.5                  32 MS
             500 Hz                   20.5                  16 MS
             1000 Hz                  20                     8 MS

             Settling time is the time in milliseconds required to obtain
             a fully valid reading after an instantaneous full-scale step.

             Effective resolution is defined as total resolution in bits minus
             RMS noise in bits. Numbers above use an oversampling factor of
             four.

             See the .doc files and the sample application source code for
             programmer's information. We will continue to add operating system
             and language support for the Model 401 as it becomes available.

             SECTION 4: TROUBLESHOOTING

             1)  Can't Connect.

                 A. Make sure that power is connected properly to the 401.
                 B. If a hub is being used, make sure the cable is not a
                     crossover cable. Otherwise make sure it is.
                 C. Cycle power to the Model 401. Wait 30 seconds, then try
                    to connect again.
                 D. If you are using a fixed IP address, verify it using PING.
                 E. If you are using BOOTP or DHCP, verify the mac address for
                    your Model 401.
                 F. The Model 401 can have the wrong IP address saved. To
                    restore the default IP address, ground digital input number
		    3 and 4 (pins 8 and 9) and cycle the Model 401's power. 
                    The IP address will always be 10.1.1.2 after that process.

                                                                         page 9

             2)  Model 401 won't respond to a data request.

                    Remember to wait for the result from the previous request
                    before issuing another.

             3)  Data is consistent, but wrong.

                 A. Do a system calibration.
                 B. Make sure another A/D input channel isn't badly over-
                    range.
                 C. Resend the rate information. If power is momentarily lost
                    to the isolated circuitry, the A/D rate will be forgotten.

             4)  Data fluctuates wildly during scanning.

                    If a data buffer overflows, your data may lose
                    registration, that is, high, middle and low bytes of
                    the answer may be confused. Stop and restart the scan, or
                    reconnect to correct the problem.

             5)  Data is noisy.

                 A. Lower the data rate or increase averaging.
                 B. Check shielding and grounding. Check that the DC common-
                    mode range of +/-6 volts is being observed.
                 C. Make sure another A/D input channel isn't badly over-
                    range.
                 D. Make sure that your power supply is not being loaded to
                    below 14 volts.

             SECTION 5: INTERNAL ADJUSTMENTS

                 Hardware calibration is set at the factory and should never
             need adjustment. The software should always be able to calibrate
             to yield peak performance.

                 There are two potentiometers on the board. The potentiometer
             closest to the power input connector is the common-mode rejection
             adjustment. The other adjusts the reference voltage. Changing the
             reference voltage has the effect of changing the gain.

                 If you wish to reset the common-mode adjustment, first
             connect the + and - input pins of a channel to a ground on the
             analog input connector. Zero the channel by using the offset
             command. Now remove the connection to ground and connect both

                                                                        page 10

             input pins to the 5 volt reference on pin 8 of the analog input
             connector. Adjust the common-mode potentiometer for a reading of
             zero. Repeat for best results.

                 The A/D gain is set by connecting a known voltage to an analog
             channel. Do a system calibration, then adjust the gain
             potentiometer to obtain the desired reading. Repeat for best
             results.

             SECTION 6: MODEL 401 SPECIFICATIONS

             A/D TYPE:                   24-bit delta-sigma converter with
                                         microcontroller supervisor and
                                         optical isolation

             MONOTONICITY:               23 bits

             LINEARITY:                  +/-0.002% of full scale

             DIFFERENTIAL INPUT RANGE:   +/-5 volts

             DC COMMON MODE RANGE:       +/-6.5 volts

             DC COMMON MODE REJECTION:   -100 dB typical

             ANALOG INPUTS:               2, multiplexed true differential
                                          protected to +/-60 volts

             INPUT IMPEDANCE:             1,000,000 megohms typical

             PROGRAMMABLE DATA RATE:      10 to 1000 Hz, lower rates are
                                          generated through digital averaging.

             EFFECTIVE RESOLUTION:       Effective resolution is defined as
                                         total resolution in bits minus RMS
                                         noise in bits. Figures below use an
                                         oversampling ratio of four.

                                       Rate    Effective Resolution in Bits
                                       ------------------------------------
                                       1000                         20
                                        100                         22
                                         50                         22.5

             SCANNING MODE:     Single, or two-channel scanning mode available.
                                Rates are crystal-controlled for accurate
                                timing. Divide rates above by 10 for speed and
                                resolution in two-channel scanning mode.

                                                                        page 11

             DIGITAL INPUTS:    8 bits, contact closure or 5 volt logic
                                compatible

             DIGITAL OUTPUTS:   8 latched, ruggedized, double-buffered 5V
                                outputs

             POWER REQUIREMENT: 14 to 30 VDC, regulated or unregulated, for
                                isolated circuitry

             TYPICAL POWER      The Model 401 requires 120 MA
             CONSUMPTION        (add drive current for active digital outputs,
                                up to 20 MA each)

             SIZE:              3.7 x 5.5 x 1.25 inches

             An optional enclosure will be offered soon.

                                  LIMITED WARRANTY

                  The Lawson Labs, Inc. Model 401 is guaranteed against
             defects in materials and workmanship for a period of one year
             from the date of delivery. Products must be returned to Lawson
             Labs for warranty service. Contact Lawson Labs at 800 321-5355
             for return authorization before returning anything for service.
                  The above warranty is in lieu of all warranties express or
             implied. Lawson Labs will not be liable for indirect or
             consequential damages caused by any defect in this product. Some
             states do not allow the limitation of consequential
             damages, so the above exclusion may not apply to you.