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Appendix A

Technical Aspects

43

Technical Description

The PowerLab provides control and low-voltage power to front-ends
through a special expansion connector called the I

2

C (eye-squared-

sea) bus. Front-ends are also connected to the analog inputs of the
recording unit via a BNC-to-BNC cable. The overall operation of the
Bridge Amps can be better understood by referring to Figure A–1.

The digital control interface used to control ﬁlter settings, gain,
coupling, and zeroing circuits uses an I

2

C interface system, which

provides a 4-wire serial communication bus to the recording unit and
other front-ends. All control of the Bridge Amp is through this bus.
Also present on the I

2

C connector is a set of power supply rails

derived from the recording unit. The Bridge Amp has its own
on-board regulators to ensure a stable power supply.

The input stage consists of a low-drift instrumentation ampliﬁer with
programmable gain (fully software-controlled). The gain of this stage
is combined with the gain of the recording unit to give a total gain of
up to 50 000 (at this ampliﬁcation, 200 μV is full scale). From the input
ampliﬁer, the signal is passed to a ﬁxed ﬁfth-order, low-pass, ﬁlter.
The ﬁlter allows a range of cutoff frequencies to be selected under
software control.

The excitation voltage output circuit is a complementary output stage,
derived from a stable internal voltage reference, capable of giving up
to ±10 volts (20 volts DC) excitation. The excitation voltage for each
channel is completely independent from other channels. The
transducer excitation voltage can be adjusted by connecting a resistor
between two pins on the plug that plugs into the Bridge Amp’s input
socket. This resistor is usually placed inside the transducer’s DIN
plug so that the transducer will always get the correct excitation
voltage when it is connected.

To remove any offsets caused by an attached transducer or signal
baseline, a DC offset circuit with a 16-bit DAC (digital-to-analog
converter). This is internally connected to the input stage. Transducer
offsets are zeroed by applying a corrective DC voltage to the input
stage via the DAC, under software control.

The DAC is only capable of producing corrective voltages in discrete
steps.

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Содержание Bridge Amp

Страница 1: ...l service in house repair center WE BUY USED EQUIPMENT Sell your excess underutilized and idle used equipment We also offer credit for buy backs and trade ins www artisantg com WeBuyEquipment REMOTE INSPECTION Remotely inspect equipment before purchasing with our interactive website at www instraview com LOOKING FOR MORE INFORMATION Visit us on the web at www artisantg com for more information on ...

Страница 2: ...Bridge Amp Owner s Guide Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE www artisantg com ...

Страница 3: ...d trademarks of Apple Computer Inc Windows Windows XP and Windows Vista are either registered trademarks or trademarks of Microsoft Corporation All other trademarks are the property of their respective owners Product ML221 Bridge Amp ML224 Quad Bridge Amp ML228 Octal Bridge Amp Document Number U ML221 OG 002B Part Number 4708 Copyright February 2008 ADInstruments Pty Ltd Unit 13 22 Lexington Drive...

Страница 4: ...Checking the Transducer 21 2 Setting Up 23 PowerLab Requirements 24 Software Requirements 24 Connecting to the PowerLab 24 Multiple Front ends 25 Using ADInstruments Programs 26 The Bridge Amp Dialog 27 3 Adapting Transducers 35 Introduction 36 Transducer Adaptations 36 Setting the Excitation Voltage 37 Wiring Up the Transducer 38 ATechnical Aspects 41 Bridge Amp Operation 42 Technical Description...

Страница 5: ...s Guide iv B Troubleshooting 45 Problems 46 C Specifications 49 Single Quad and Octal Bridge Amps ML221 ML224 ML228 49 Index 51 Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE www artisantg com ...

Страница 6: ...o product is intended for the prevention curing or alleviation of disease injury or handicap Where a product meets IEC 60601 1 it is under the principle that it is a more rigorous standard than other standards that could be chosen and it provides a high safety level for subjects and operators The choice to meet IEC 60601 1 is in no way to be interpreted to mean that a product is a medical device m...

Страница 7: ...ctors are suitable for connection to human subjects even when there is direct electrical connection to the heart Warning symbol The exclamation mark inside a triangle means that the supplied documentation must be consulted for operating cautionary or safety information before using the device Further information is available on request Bio Amp Safety Instructions The Bio Amp inputs displaying any ...

Страница 8: ...ted However they can produce pulses of up to 100 V at up to 20 mA Injury can still occur from careless use of these devices Several points must be observed for safe operation of the Isolated Stimulator The Isolated Stimulator output must only be used with the supplied bar stimulus electrode The Isolated Stimulator output must not be used with individual physically separate stimulating electrodes S...

Страница 9: ...on the front panel of any built in Isolated Stimulator or the ML180 Stimulus Isolator The ML180 Stimulus Isolator is supplied with a special transformer plug pack The plug pack complies with medical safety requirements Therefore under no circumstances should any other transformer be used with the Stimulus Isolator For a replacement transformer plug pack please contact your nearest ADInstruments re...

Страница 10: ... subject APPLIED PARTS may be recognized by the BF or CF symbols which appear in the Safety Symbols section of these Safety Notes Only CF rated APPLIED PARTS must be used for direct cardiac connection Never connect parts which are marked as an APPLIED PART to those which are not marked as APPLIED PARTS Do not touch the subject to which the PowerLab or its peripherals is connected at the same time ...

Страница 11: ...lowing constraints They shall not be placed on the ﬂoor Additional multiple portable socket outlets or extension cords shall not be connected to the system They shall only be used for supplying power to equipment which is intended to form part of the system Cleaning and Sterilization ADInstruments products may be wiped down with a lint free cloth moistened with industrial methylated spirit Refer t...

Страница 12: ...ly with such testing you should contact your PowerLab representative to arrange for the equipment to be checked and serviced Do not attempt to service the device yourself Environment Electronic components are susceptible to corrosive substances and atmospheres and must be kept away from laboratory chemicals Storage Conditions Temperature in the range 0 40 C Non condensing humidity in the range 0 9...

Страница 13: ...Bridge Amp Owner s Guide 12 Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE www artisantg com ...

Страница 14: ... DC bridge transducers including commonly available force transducers temperature probes light meters displacement transducers pressure transducers and similar devices This chapter provides an overview of the various Bridge Amps describes their basic features and looks at which transducers can be used with them 1 Overview Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE ww...

Страница 15: ... tilt it gently from side to side and listen for anything that appears to be loose If you have found a problem contact your authorized ADInstruments representative immediately and describe the problem Arrangements can be made to replace or repair the front end Front end Fundamentals The PowerLab system consists of a recording unit and application programs that run on the computer to which the unit...

Страница 16: ...rce transducers temperature probes light meters displacement transducers pressure transducers and similar devices There are several models of Bridge Amp The Bridge Amp provides just one connection for a bridge transducer the Quad Bridge Amp provides four connections for bridge transducers and the Octal Bridge Amp provides eight connections for bridge transducers Grass transducers can connect to an...

Страница 17: ...he front panel and the Status indicators of the Quad Bridge Amp and Octal Bridge Amp are located beneath each connector on the front panel When an ADInstruments program such as LabChart starts up the Status indicator light should glow green indicating that the program has found the front end checked and selected it and is ready to use it If the light does not glow when the program is running this ...

Страница 18: ...o the Troubleshooting section of this Owner s Guide For the overload indicator to function power must be applied to the Bridge Amp via a PowerLab LabChart software does not need to be loaded When a software application is running and a channel is being zeroed the Status indicators for the other channels should temporarily be off The Back Panel The back panel of the Bridge Amp provides all the sock...

Страница 19: ...nfusion if you do A BNC to BNC cable is supplied for each connection UsingTransducers Bridge Amps are designed to allow the PowerLab to connect to most DC bridge transducers including commonly available force pressure and displacement transducers temperature probes light meters and similar devices They are capable of supporting various powered transducers and certain low impedance unpowered or sel...

Страница 20: ...ase provide ADInstruments with an accurate circuit of the transducer and a sample and we will see about testing the device for compatibility Half bridge transducers will need to be wired up with compensating resistors before they can be used with any of the Bridge Amps see Chapter 3 DC Strain gauge These are full bridge or half bridge transducers requiring a DC excitation voltage and output voltag...

Страница 21: ...rk The Bridge Amp can connect to most bridge type transducers hence its name The term bridge refers to the circuit conﬁguration that is normally called a Wheatstone bridge These transducers come in two forms full bridge and half bridge Some explanation is given here of bridge type transducers although there are of course other types that work differently such as the semiconductor transducer The fu...

Страница 22: ...maximum excitation voltage or recommended range is for the transducer 2 The conﬁguration of the transducer wiring connections 3 If the transducer is a bridge type transducer and whether it has a full bridge or half bridge conﬁguration Transducers supplied by ADInstruments are supplied pre adjusted and need no adjustment Do not attempt to connect the signal leads from the transducer to the Bridge A...

Страница 23: ...ance and output voltage Such transducers do not need the excitation range to be adjusted from the default setting If they have low output voltages though then it is possible that their offset ranges require adjusting Using Grass Transducers with DIN Bridge Amps Most Grass transducers should have an impedance of about 350 Ω or so A few Grass and Grass compatible transducers have a much lower impeda...

Страница 24: ...quick test to make sure that it is working properly The best way to conﬁgure your system for one or more front ends is discussed along with how to use the Bridge Amp with ADInstruments application software 2 Setting Up Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE www artisantg com ...

Страница 25: ...e Connecting to the PowerLab Connect your Bridge Amp to the PowerLab as follows Ensure that the PowerLab is turned off Failure to do this may damage the PowerLab the Bridge Amp or both Connect the I2 C output of the PowerLab to the I2 C input of the front end using the I2 C cable provided Connect a BNC cable from each signal output on the rear of the Bridge Amp to an input on the front panel of th...

Страница 26: ... Figure 2 2 The BNC cable for each front end is connected to one of the inputs of the PowerLab except where otherwise speciﬁed PowerLabI2 Coutput Front endI2 Cinput I2 Cconnectorcable BNCconnectorcable Front endsignaloutput PowerLabI2 Coutput Front endI2 Cinputs Front endI2 Coutput Figure 2 2 Connecting multiple front ends to the PowerLab two single front ends shown for simplicity Figure 2 1 Conne...

Страница 27: ...n the LabChart or Scope folder LabChart for Windows has them built in and Scope for Windows has them in the Essential Files folder in the Scope folder To replace the drivers you generally need to reinstall the ADInstruments software The Bridge Amp Self test Once the Bridge Amp is properly connected to the PowerLab and when the proper software is installed on the computer a quick check can be perfo...

Страница 28: ...ridge Amp Dialog The Bridge Amp dialog allows software control of the various ampliﬁers and ﬁlters in the Bridge Amp and PowerLab for an input The signal present at a PowerLab input is displayed so that you can see the effects of changes straight away Once the settings in the dialog are changed click OK to apply them To set up many inputs quickly click the arrows at the top of the dialog or use th...

Страница 29: ...nsfilter Averagesignal value Pause Scroll button Inputselection Displaysavoltmeteronscreenforuse whensettingtheoffsetexternally Displaysthe UnitsConversiondialog Settheoffsetfor theBridgeAmp Rangepop up Mainsfilter Figure 2 3 The Bridge Amp dialog for Windows before zeroing Figure 2 4 The Bridge Amp dialog for Macintosh after zeroing Artisan Technology Group Quality Instrumentation Guaranteed 888 ...

Страница 30: ...ovided are appropriate to the type of transducers used with the Bridge Amp and the signals usually measured which tend to be of lower frequency Low pass ﬁlters allow you to remove high frequency components such as noise from an input signal The Mains ﬁlter allows you to remove interference at the mains frequency typically 50 or 60 Hz Low Pass Filtering The Low Pass pop up menu provides a choice of...

Страница 31: ...t fully effective in the ﬁrst second of each data block Anti alias Click the Anti alias checkbox to turn anti aliasing on and off Aliasing is distortion caused by frequencies of the incoming biological waveform that are more than half the sampling frequency If you monitor physiological signals with a low pass ﬁlter setting of 100 Hz but you are only sampling at 100 Hz aliasing may cause the record...

Страница 32: ...imuli The offset controls in the Bridge Amp dialog can be used to zero the reading manually or automatically Manual Zeroing The up and down arrows near the Zero button allow manual adjustment of the signal offset Click the up arrow to shift the signal positively and the down arrow to shift it negatively The shift by clicking the arrow buttons depends on the range setting At high ranges the increme...

Страница 33: ...he positive or negative corrective adjustment On a Macintosh click the small 0 button to restore the offset circuit to its initial non zeroed position and the offset display value to zero This can be used to determine the offset generated by a transducer Display Offset Click Display Offset to display the Input Value dialog Figure 2 6 A voltmeter displays the voltage currently being measured for an...

Страница 34: ...ialog is transferred to the data display area of the Units Conversion dialog Use the Pause button to capture a speciﬁc signal The units conversion only applies to subsequently recorded signals so it is more limited than choosing Units Conversion from a Channel Function pop up menu as it does not allow conversion of individual blocks or pages of data Artisan Technology Group Quality Instrumentation...

Страница 35: ...Bridge Amp Owner s Guide 34 Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE www artisantg com ...

Страница 36: ... powered third party transducers with your Bridge Amp you may need to adapt them using the information provided here NOTE Please ensure that any modiﬁcations made to transducers are carried out by experienced technical staff as incorrect wiring may damage the transducer or Bridge Amp If you are unsure please contact your nearest ADInstruments representative for further assistance 3 Adapting Transd...

Страница 37: ...your Bridge Amp If you have little experience with electronics and no technician to assist you your ADInstruments representative should be able to help Types of Bridge Amp and Adaptation The ML118 Quad and ML119 Octal Bridge Amps have a ﬁxed excitation voltage of 8 V 4 V with respect to ground You cannot adjust the offset voltage range of the zeroing circuit for these front ends Adapting powered t...

Страница 38: ...en the transducer is plugged into the Bridge Amp To program the excitation voltage for a particular transducer choose a value of resistance from Table 3 1 to match the required excitation voltage for your transducer In most cases you should be able to get close to the required excitation voltage by selecting one of those values We recommend that the excitation resistor be 0 25 or 0 125 Watt 2 or 1...

Страница 39: ...owered transducer for use with the Bridge Amp is to wire the transducer to the DIN plug There are several things to note when wiring up transducers 1 Make sure that the transducer wiring passes through the casing before soldering the wires to the plug 2 The transducer wires should be cut stripped and tinned prior to soldering to ensure a good connection 3 The pin numbers shown in the diagrams are ...

Страница 40: ...ed to the shield The Finished Transducer After connecting the excitation voltage programming resistor and wiring up the transducer to the DIN plug the transducer should now be fully conﬁgured for your application The excitation voltage will be set automatically when you plug the transducer into the Bridge Amp 1 2 3 4 5 6 7 8 Excitation voltage programming resistor Groundorcentretap shield Signalpo...

Страница 41: ...Bridge Amp Owner s Guide 40 Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE www artisantg com ...

Страница 42: ...here to use the Bridge Amp It is likely to be of special interest to the technically minded indicating what the Bridge Amp can and cannot do and its suitability for particular applications You should not use it as a service manual user modiﬁcation of the equipment voids your rights under warranty A Technical Aspects Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE www arti...

Страница 43: ...tering to remove unwanted signal frequencies a stable DC excitation voltage supply for powering the transducer digitally controlled transducer zeroing circuitry Figure A 1 Block diagram of the ML221 Bridge Amp The ML224 and 228 Bridge Amps are similar but with four or eight inputs respectively Gain control Prog Amp 16 bit DAC Bridge excitation driver Pre amp Vref Transducer signal inputs Excitatio...

Страница 44: ... at this ampliﬁcation 200 μV is full scale From the input ampliﬁer the signal is passed to a ﬁxed ﬁfth order low pass ﬁlter The ﬁlter allows a range of cutoff frequencies to be selected under software control The excitation voltage output circuit is a complementary output stage derived from a stable internal voltage reference capable of giving up to 10 volts 20 volts DC excitation The excitation v...

Страница 45: ...Bridge Amp Owner s Guide 44 Artisan Technology Group Quality Instrumentation Guaranteed 888 88 SOURCE www artisantg com ...

Страница 46: ...ter and the guide to your PowerLab may contain possible solutions If none of the solutions here or elsewhere are of help then consult your ADInstruments representative Most of the problems that users encounter are connection problems and can usually be ﬁxed by checking connections and starting up the hardware and software again Very rarely will there be an actual problem with the Bridge Amp or the...

Страница 47: ...e BNC or I2 C cable is faulty Replace the cable and try again Immediately label all cables proved faulty so that you don t use them again by accident The Bridge Amp is faulty This is the least likely event If the Bridge Amp will not work properly after the previous measures then try using it on another PowerLab If the Bridge Amp s Status indicator fails to light with a second PowerLab the Bridge A...

Страница 48: ...ls to light with a second PowerLab the Bridge Amp may be faulty Contact your ADInstruments representative to arrange for repairs The trace will not zero properly when using the automatic or manual zeroing controls Variations in the transducer signal during auto zeroing may cause the software to fail to zero the offset properly if it zeroes at all Make sure that the transducer is kept still and tha...

Страница 49: ...e that the particular channel in LabChart has been correctly recognized as a Bridge Amp and not as Input Ampliﬁer The transducer itself is faulty Check the transducer with another Bridge Amp if possible and try again Contact the supplier or manufacturer of the transducer if there still seems to be a problem The signal from the transducer drifts excessively Both the Bridge Amp and transducer requir...

Страница 50: ...4 steps combined PowerLab and Bridge Amp 5 V 2 V 1 V 500 mV 200 mV 100 mV 50 mV 20 mV 10 mV 5 mV 2 mV 1 mV 500 μV 200 μV Ampliﬁcation accuracy 0 5 combined PowerLab and Bridge Amp Maximum input voltage 10 volts Input impedance 2 1 MΩ single ended 2 MΩ differential Low pass ﬁltering 1 Hz to 1 kHz in seven steps software selectable C Specifications Artisan Technology Group Quality Instrumentation Gu...

Страница 51: ... about 0 V 1 2 5 V 310 μ V step 100 mV 200 mV 500 mV 31 μ V step 200 μV to 50 mV 3 μV step Control Port I2C port Power and control bus for front end units Supports a number of front ends dependent on the PowerLab Interface communications rate of 50 kbits s Physical Configuration Weight and Dimensions h w d Single ML221 50 mm 76 mm 260 mm 1 97 3 0 10 2 710 g Quad ML224 60 mm 200 mm 250 mm 2 36 7 9 ...

Страница 52: ...g converter 43 DIN socket 16 display offset 32 E excitation overload 17 excitation voltage 36 37 38 F filtering 29 front panel 15 17 front end driver 26 47 front ends general 14 15 full bridge transducers 20 38 39 H half bridge transducers 20 how transducers work 20 21 I impedances maximum 19 input socket 16 I2C bus 15 17 43 L LabChart 26 M maintenance 10 manual zeroing 31 O offset adjustment 31 3...

Страница 53: ...ezoelectric 20 semiconductor 19 transducers adapting 35 39 checking 21 DIN 36 39 full bridge 20 38 39 Grass 22 half bridge 20 how they work 20 21 suitable 19 unsuitable 20 U unsuitable transducers 20 user modification 41 using ADInstruments programs 26 33 using this guide 14 V voltmeter 32 Z Zero button 32 zeroing 31 32 automatic 31 manual 31 Artisan Technology Group Quality Instrumentation Guaran...

Страница 54: ...l service in house repair center WE BUY USED EQUIPMENT Sell your excess underutilized and idle used equipment We also offer credit for buy backs and trade ins www artisantg com WeBuyEquipment REMOTE INSPECTION Remotely inspect equipment before purchasing with our interactive website at www instraview com LOOKING FOR MORE INFORMATION Visit us on the web at www artisantg com for more information on ...

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