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Teledyne 235 Скачать руководство пользователя страница 6

Teledyne Analytical Instruments

1-2

1 Introduction

Model 235

Because analysis by thermal conductivity is not an absolute measure-

ment, standardization gases of

known composition

will be required to fix

the upper and lower parameters of the range (or ranges) of analysis. These
gases will be used to periodically check the

accuracy of the analyzer.

The difference in thermal conductivity between the fixed reference gas

and the sample is sensed by hot wire elements. The elements are mounted in
a cell assembly so that one set is in the reference and the other in the sample
stream. Each set of elements is a component in an electrical bridge circuit.

During calibration, the bridge circuit is balanced in zero and reference

gas at one end of the measurement range, and sensitized in reference and
span gas at the other end, so that intervening points along the range (or
ranges) of interest will produce a DC electrical signal representative of the
analysis. The resulting electrical signal is fed to an amplifier and span pot,
which produce a standard 0-1V output signal. An E to I converter PC board
is also installed and produces an isolated 4–20 mA DC current output in
addition to the voltage output.

The temperature of the measuring cell is regulated to within 0.1 degree

C by a sophisticated control circuit. A thermistor is used to measure the
temperature, and a zero-crossing switch regulates the power in a cartridge-
type heater. Temperature control is precise enough to eliminate diurnal
effects in the output over the operating ranges of the analyzer.

The overall design of the instrument is intended to facilitate servicing

and troubleshooting, should that ever be necessary. The controls are all
mounted on the front panel, which can swing down, allowing access to the
cell compartment. The cell is enclosed in an insulated compartment that is
readily removable from the chassis; the electronics are mounted on a series
of circuit boards at the rear of the enclosure, accessible by removing the
back panel.

Explosion-proof models of the series use sealed explosion-proof

enclosures for the analysis section (Model 237) or both the analysis section
and control unit (Model 238). Model 235 is general purpose with remote
control unit, and Model 235 is general purpose with integral control unit.

1.1

Electronic Circuitry

The electronic components are mounted on a number of circuit boards

that plug into sockets on a larger board, dubbed the “Mother Board”. This
allows for rapid troubleshooting and repair of any defective parts, and also
for rapid field installation of optional features not ordered with the unit.

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Содержание 235

Страница 1: ...ESENTINTHISMONITORINGSYSTEM PERSONALPROTECTIVEEQUIPMENTMAYBEREQUIREDWHENSERVICINGTHISSYSTEM HAZARDOUSVOLTAGESEXISTONCERTAINCOMPONENTSINTERNALLYWHICHMAYPERSISTFORA TIMEEVENAFTERTHEPOWERISTURNEDOFFANDDISCONNECTED ONLY AUTHORIZED PERSONNEL SHOULD CONDUCT MAINTENANCE AND OR SERVICING BEFORE CONDUCTINGANYMAINTENANCEORSERVICINGCONSULTWITHAUTHORIZEDSUPERVISOR MANAGER DANGER P N M32845 08 06 99 ECO 99 032...

Страница 2: ... of any parts in so far as such alterations do not adversely affect our warranty ImportantNotice This instrument provides measurement readings to its user and serves as a tool by which valuable data can be gathered The information provided by the instrument may assist the user in eliminating potential hazards caused by his process however it is essential that all personnel involved in the use of t...

Страница 3: ...40 Volt Operation optional 1 4 2 Installation 2 1 Location 2 1 2 2 Electrical Connections 2 1 2 3 Gas Connections 2 2 2 3 1 Reference and Zero Gas 2 2 2 3 2 Vent Lines 2 2 2 4 Pressure Regulation 2 3 2 5 Accessory Sample System Components 2 4 2 6 Recommended Flowmeter Readings 2 5 3 Operation 3 1 Preliminary 3 1 3 2 Gas Flowrate 3 1 3 3 Zero Standardization 3 1 3 4 Span standardization 3 2 3 5 Ons...

Страница 4: ...leaks always exist The customer should ensure that the principles of operating of this equipment is well understood by the user Misuse of this product in any manner tampering with its components or unauthorized substitution of any component may adversely affect the safety of this instrument Since the use of this instrument is beyond the control of Teledyne no responsibility by Teledyne its affilia...

Страница 5: ...zer and a control manifold will be required for the intro duction of zero and span gas as well as sample gas into the sample path Appropriate pressure reducing regulators will have to be installed at all gas supply sources for those customers wishing to incorporate their own sample controls a recommended system piping schematic is included among the drawings at the rear of the manual Thermal condu...

Страница 6: ... temperature of the measuring cell is regulated to within 0 1 degree C by a sophisticated control circuit A thermistor is used to measure the temperature and a zero crossing switch regulates the power in a cartridge type heater Temperature control is precise enough to eliminate diurnal effects in the output over the operating ranges of the analyzer The overall design of the instrument is intended ...

Страница 7: ...ndard features 1 2 1 T C Cell Power Supply Amplifier Board This circuit contains an IC regulator that holds the voltage through the cell to 4 5 V It also contains a 2 stage IC amplifier with range resistors 1 2 2 Differential Power Supply Board 15 Volts regulated for electronic amplifiers etc and 24 volts non regulated for alarm and relay circuitry and certain other functional uses are supplied by...

Страница 8: ...rd optional An excellent alternative to the use of correction curves is available as an option with the Series 235 Analyzer A digital linearizer circuit is avail able as a plug in PC board This is a very flexible circuit that produces a linear correction to a wide variety of non linear curves The result is an output signal which is linear over the specified analysis range or ranges When employed t...

Страница 9: ... location and identification of the gas line and electrical conduit connections as well as the physical dimensions of the analyzer case is included in the drawings at the rear of the manual 2 2 Electrical Connections A single phase 110 to 120 Volt or 220 to 240 Volt 50 or 60 Hz line capable of delivering 2 1 2 amperes of current continuously is required to operate the analyzer Primary power connec...

Страница 10: ... This elimi nates the need to have reference gas constantly passing through the cell For instruments equipped with the optional sealed air reference there will not be reference inlet or vent ports A supply of gas containing little or none of the components of interest is required to zero standardize the analyzer In order to satisfy the requirements both of these gases must be supplied from purchas...

Страница 11: ... barometric pressure changes 4 The vent lines must be installed so that water and dirt cannot accumulate in them 2 4 Pressure Regulation All incoming gas lines should be equipped with pressure regulators The sample line pressure regulator should be installed as close to the sample point as possible to minimize sample line lag time Sample pressure should be set somewhere between 5 and 50 psig 10 ps...

Страница 12: ...lving 0 08 SCFH 40 to 50 cc min for the reference path of the analyzer 3 Select a flowmeter capable of resolving 0 3 SCFH 150 cc min for the sample path of the analyzer See Addendum A for recommended flowmeter readings for gases heavier or lighter than air 2 6 Recommended Flowmeter Readings for Gases Heavier or Lighter Than Air Due to the wide range of applications and gases that are measured with...

Страница 13: ...urements should be made at the same flowrate used when calibrating the analyzer TBE recommends for lighter than air gas backgrounds setting the flowmeter to a lower reading for reference and measurement this will conserve gas For example for hydrogen or helium set the flowmeter reading to 0 1 SCFH A higher reading is recommended for heavier than air gas backgrounds e g for carbon dioxide or argon ...

Страница 14: ...Teledyne Analytical Instruments 2 6 2 Installation Model 235 Series ...

Страница 15: ...just the flowrate to approximately 0 3 SCFH 150 cc min See Section 2 6 for additional flowrate information for gases lighter or heavier than air Allow the analyzer to run with zero and reference gas flowing for several hours before attempting calibration This will permit the cell to come tothermalequilibrium 3 3 Zero Standardization After the necessary temperature stabilization period the analyzer...

Страница 16: ...ny contained in the zero gas 3 4 Span Standardization After the zero setting has been accomplished the span or sensitivity of the analyzer can be checked as follows 1 Arrange the sample path so that span gas is flowing through the analyzer 2 Check the sample path flowmeter to see if the span gas is flowing at a 0 3 SCFH rate 3 With mufti range instruments set the range selector switch on the posit...

Страница 17: ...upply cylinder periodically to insure against accidental depletion Whenever it is necessary to replace the reference gas supply the analyzer standardization procedures must be repeated Standardization The analyzer should be restandardized on a monthly schedule as a check of its performance 3 7 Maintenance Since there are no moving parts in the analyzer no routine mainte nance is required other tha...

Страница 18: ...Teledyne Analytical Instruments 3 4 3 Operation Model 235 Series ...

Страница 19: ... zero zero is the starting point of the curve Refer to Figures 4 1 4 2 and 4 3 The error left after linearization is due to the curvature of each individual section This error can be made quite small by correct selec tion of the breakpoints The output of the linearizer is 0 1 Volt See Figure 4 4 to visualize the linearization process Figure 4 5 shows how the linearizer works in actuality It is exa...

Страница 20: ...ION The Linearizer output is proportional to its input in a complimentary fashion to the analyzer curve As a result the output is directly proportional to the parameter being measured Figure 4 1a THE PROBLEM The analyzer output is not directly proportional to the parameter it is supposed to measure ...

Страница 21: ... Analyzer Linearizer 4 Figure 2a THE IMPLEMENTATION STEP 1 Adjust the gain of the first amplifier to bring the first segment from 0 to 1 of the analyzer curve into line with the ideal curve This produces a small error in the first section but a larger error at higher inputs ...

Страница 22: ... 4 2b THE IMPLEMENTATION STEP 2 At point 1 the second amplifier begins to work in addition to the first Its gain is adjusted so that point 2 lies on the ideal curve The error is small until point 2 is reached Here the large error is due to the curvature of the original analyzer curve ...

Страница 23: ...lyticalInstruments Thermal Conductivity Analyzer Linearizer 4 FIGURE 4 2c THE IMPLEMENTATION STEP 3 At point 2 the third amplifier begins to work in addition to the first two Its gain is adjusted so that point 3 lies on the ideal curve ...

Страница 24: ...NEERING AnalyticalInstruments 4 6 4 Linearizer Model 235 Figure 4 3 THE RESULT By using all the line segment amplifiers the output of the analyzer is made to be almost directly proportional to the parameter being measured ...

Страница 25: ...4 7 TELEDYNE BROWN ENGINEERING AnalyticalInstruments Thermal Conductivity Analyzer Linearizer 4 Figure 4 4 The Effect of Each Amplifier on the Final Result The points labeled 1 2 3 etc are breakpoints ...

Страница 26: ...TELEDYNE BROWN ENGINEERING AnalyticalInstruments 4 8 4 Linearizer Model 235 Figure 4 5 Exaggerated Illustration of How the Linearizer Works ...

Страница 27: ...s shown in Figure 4 6 The effect of the breakpoints and trimpots can then readily be seen if you alternate the gain of the stages a jagged step effect can be produced This will show the breakpoints clearly Alterna tively a DVM may be attached to the junction of D2 and R20 this junction point accesses the output of a line segment amplifier As the input voltage is gradually increased the DVM at some...

Страница 28: ...ximum If the vertical scale and the timebase are arranged so that the slope of the unmodified triangle wave is 45 degrees and the amplitude of the wave is 2 Volts peak to peak then the value of the breakpoints may be read off the screen by measuring the distance For example say the distance measured is X Then the value of the breakpoint is X times the Volts per centimeter appropriate to the range ...

Страница 29: ...g signals however do not get through D1 but can go through D2 and R20 then acts as a feedback resistor to set the gain of the circuit to 4 in the example for A1C Since D2 is inside the feedback loop its voltage drop does not appear at the output R6 sums a fraction of the 15 V supply to the input voltage the output of the circuit is thus Vo R20 Vin R7 15 R6 for V0 O Vo O if R20 Vin R7 15 R6 O From ...

Страница 30: ...rmine how much signal goes directly into the summing input of A3B and now much goes through the inverter If the slider is up at the top almost all of the output of AlC will add to the output of A1D If the slider is down at the bottom then the output of A1C will be subtracted from that of AlD If the slider is in the middle the output will be added and subtracted in the same amount and thus will hav...

Страница 31: ...y curved Since the linearizer is to approximate the curve with a series of straight lines we would like to have most of the segments on the curved segment i e between 1 and 2 This means that most of the breakpoints must be between 1 and 2 rather than evenly spaced out Similarly for the S curve shown in Figure 4 9 the breakpoints would be concentrated between the points 1 2 and 3 4 The resistors fo...

Страница 32: ...TELEDYNE BROWN ENGINEERING AnalyticalInstruments 4 14 4 Linearizer Model 235 Figure 4 8 A Simple Curve ...

Страница 33: ...4 15 TELEDYNE BROWN ENGINEERING AnalyticalInstruments Thermal Conductivity Analyzer Linearizer 4 Figure 4 9 An S Shaped Curve ...

Страница 34: ...TELEDYNE BROWN ENGINEERING AnalyticalInstruments 4 16 4 Linearizer Model 235 Figure 4 10 Typical Component Placement on Linearizer ...

Страница 35: ...nnect the DVM to the output of the linearizer pin 7 of A3B 3 Adjust trimpot P10 until the DVM reads 0 mV 10 mV 4 4 3 Linearizing the Calibration Curve The calibration curve must be known at this point and found to be non linear This calibration can be done using known samples The curve has been studied and breakpoint positions determined on the most curved portions of the curve Appropriate breakpo...

Страница 36: ...he values obtained at various concentrations are linearlydisplayed 8 If the linearity is not quite satisfactory determine which line segment requires touch up If more than one segment is not properly adjusted readjust the segment closest to zero first All other following segments must be toucned up since they are affected by the former one If results are still not satisfactory re evaluate the brea...

Страница 37: ...OARD ETOICONVERTER ISOLATED4 20mAdc 5 F 10 FUSE 2A 220VUSEF 9 5 F 75 FUSE 1 2A 110V 220V 1 H 158 HEATER 110V 220V 1 A 31157 CELLASSEMBLY 1 A 33748 THERMISTORASSEMBLY Theseitemsareoptionstothestandardinstrumentandunlessordered willnotbepresent IMPORTANT Ordersforreplacementpartsshouldincludethepart number themodel andserialnumbersoftheanalyzer in which they are to be used Ordersshouldbesentto TELED...

Страница 38: ... components ______________________ Output Signal ______________________ Reference and Zero Gas ______________________ Note If the zero gas contains a known or equivalent impurity the zero control should be set so that the analyzer indi cates the impurity during the standardization procedure Span Gas ______________________ Selected Resistor Values ______________________ ______________________ _____...

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