Teledyne 514 User Manual
INSTRUCTION MANUAL
MODEL 514
NDIR
A
NALYZER
DANGER
HIGHLY TOXIC AND OR FLAMMABLE LIQUIDS OR GASES MAY BE PRESENT IN THIS MONITORING
SYSTEM.
PERSONAL PROTECTIVE EQUIPMENT MAY BE REQUIRED WHEN SERVICING THIS SYSTEM.
HAZARDOUS VOLTAGES EXIST ON CERTAIN COMPONENTS INTERNALLY WHICH MAY PERSIST FOR
A TIME EVEN AFTER THE POWER IS TURNED OFF AND DISCONNECTED.
ONLY AUTHORIZED PERSONNEL SHOULD CONDUCT MAINTENANCE AND/OR SERVICING. BEFORE
CONDUCTING ANY MAINTENANCE OR SERVICING CONSULT WITH AUTHORIZED SUPERVISOR/
MANAGER.
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies
P/N M63700
08/06/99
ECO # 99-0323
Copyright © 1999 Teledyne Analytical Instruments
All Rights Reserved. No part of this manual may be reproduced, transmitted,
transcribed, stored in a retrieval system, or translated into any other language or computer language in whole or in part, in any form or by any means, whether it be electronic, mechanical, magnetic, optical, manual, or otherwise, without the prior written
consent of Teledyne Analytical Instruments, 16830 Chestnut Street, City of Industry, CA
91749-1580.
Warranty
This equipment is sold subject to the mutual agreement that it is warranted by us
free from defects of material and of construction, and that our liability shall be limited to
replacing or repairing at our factory (without charge, except for transportation), or at
customer plant at our option, any material or construction in which defects become
apparent within one year from the date of sale, except in cases where quotations or
acknowledgements provide for a shorter period. Components manufactured by others
bear the warranty of their manufacturer. This warranty does not cover defects caused by
wear, accident, misuse, or neglect. We assume no liability for direct or indirect damages
of any kind and the purchaser by the acceptance of the equipment will assume all
liability for any damage which may result from its use or misuse.
We reserve the right to employ any suitable material in the manufacture of our
apparatus, and to make any alterations in the dimensions, shape or weight of any parts,
in so far as such alterations do not adversely affect our warranty.
Important Notice
This instrument is intended to be used a tool to gather valuable data. The information provided by the instrument may assist the user in eliminating potential hazards
caused by the process that the instrument is intended to monitor; however, it is essential
that all personnel involved in the use of the instrument or its interface with the
process being measured be properly trained in the process itself, as well as all
instrumentation related to it.
The safety of personnel is ultimately the responsibility of those who control
process conditions. While this instrument may be able to provide early warning of
imminent danger, it has no control over process conditions, and can be misused. In
particular, any alarm or control system installed must be tested and understood, both as
they operate and as they can be defeated. Any safeguards required such as locks, labels,
or redundancy must be provided by the user or specifically requested of Teledyne.
The purchaser must be aware of the hazardous conditions inherent in the
process(es) he uses. He is responsible for training his personnel, for providing hazard
warning methods and instrumentation per the appropriate standards, and for ensuring
that hazard warning devices and instrumentation are maintained and operated properly.
TAI, the manufacturer of this instrument, cannot accept responsibility for conditions beyond its knowledge and control. No statement expressed or implied by this
document or any information disseminated by the manufacturer or his agents is to
be construed as a warranty of adequate safety control under the user's process
conditions.
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Table of Contents
1.0 Introduction
1.1 Method of Analysis............................................................1-1
1.2 Modules (Condulets) .........................................................1-2
1.2.1 Source Module .......................................................1-5
1.2.2 Sample Module ..................................................1-5
1.2.3 Power Module ..................................................1-5
1.2.4 Detector Module ..................................................1-5
1.2.5 Local Meter Readout ..............................................1-6
1.2.6 Control Module ..................................................1-6
1.3 Typical Applications ..........................................................1-6
2.0 Operational Theory
2.1 Circuit Description.............................................................2-2
2.1.1 Source Module .................................................... 2-2
2.1.2 Sample Module ..................................................2-3
2.1.3 Power Module ..................................................2-4
2.1.4 Detector Module ..................................................2-8
2.1.5 Control Module ..................................................2-10
3.0 Installation
3.1 Location ............................................................................3-1
3.2 Sample Saction Installation...............................................3-1
3.2.1 Filtering ..................................................................3-1
3.2.2 Effluent Return........................................................3-2
3.2.3 Flow Control ...........................................................3-2
3.2.4 Selector Manifold....................................................3-3
3.2.5 Automatic Zero Operation.......................................3-3
3.3 Electrical Installation .........................................................3-3
3.3.1 Power Check..........................................................3-3
3.4 Analysis Unit .....................................................................3-5
3.5 Optical Alignement............................................................3-6
4.0 Operations
4.1 Control Functions..............................................................4-1
4.1.1 General Purpose Version: Analysis Section...........4-1
4.1.2 General Purpose Version: Controle Module...........4-2
4.1.3 Explosion-Proof Version: Control Module ..............4-3
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4.2 Start-up..............................................................................4-4
4.2.1 Preliminary Inspection............................................4-4
4.2.2 Pre-Start-up Electrical Checkout ............................4-5
4.2.3 Power On Observation ...........................................4-5
4.3 Calibration.........................................................................4-6
5.0 Maintenance & Troubleshooting
5.1 Replacement of Sample Cell Optics .................................5-2
5.2 Replacement of Filter Wheel Optics..................................5-2
5.3 Replacement of Source Lamp Assembly ..........................5-3
5.4 Replacement of Filter Position Sensor..............................5-4
5.5 Replacement of Preamplifier Circuitr Card........................5-4
5.6 Re-screening of Lens ..................................................5-5
5.7 Troubleshooting ..................................................5-5
Appendix
Specifications ....................................................................A.1
Application Data ................................................................A.2
Recommended Spare Parts List .......................................A.3
Drawing List ......................................................................A.4
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Introduction 1.0
1.0 Introduction
The Model 514 Photometric Analyzer measures the concentration of
one component in a mixture of liquids or gases continuously by measuring
the radiation absorbed in selected bands in the near infrared (NIR) spectral
region. Most liquids or gases having a characteristic absorption spectrum in
this region can be measured with the analyzer. When we refer to the NIR
region we mean that portion of the electromagnetic energy spectrum from
1.0 to 2.8µ. This range can be extended to somewhat longer wavelengths
using special detectors. Most organic and some inorganic compounds can be
analyzed in the NIR region.
For example, the 514 is used to analyze parts per million (PPM) or the
percentage concentration of water in a variety of compounds (see Typical
Applications). The analyzer can also be used to measure the concentration of
one organic compound in the presence of another organic compound.
1.1 Method of Analysis
The 514 contains an optical system consisting of a quartz iodine source
lamp for NIR energy emission, collimating lens, sample cell and detector.
Isolator or light beam tubes filled with nitrogen gas interconnect the source
and sample, and sample and detector modules. In front of the detector is a
motor-driven filter wheel containing two optical interference-type filters,
located 180° from each other. These filters, designated the reference and
measuring filters, are alternately and continuously rotated in and out of the
optical path. The sample flows continuously through the sample cell absorbing energy at various wavelengths throughout the NIR spectrum. The wavelengths and intensities of absorption peaks throughout the spectrum are
characteristic of the specific compounds that are present in the sample.
In any photometric analysis, there is always the component that we are
interested in analyzing, and background components that we are not interested in measuring. Both the component of interest and the background
component may have complex NIR absorption spectra.
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1–1
1.0 Introduction
The quantitative measurement of a compound using the 514 is based on
Beer’s Law, which states that the intensity of a beam of monochromatic
radiation transmitted through a sample decreases exponentially as the concentration of the absorbing sample increases.
To approximate monochromatic radiation, a specific wavelength is
isolated by the use of the interference-type filters. The filters allow transmission of NIR over a narrow band pass region of the NIR spectra and completely block all other wavelengths. Proper selection of the measuring and
reference filter wavelengths allows the accurate isolation and measurement
of the component of interest.
The use of two filters allows cancellation of energy changes due to
turbidity, dirty sample cell windows, and aging of the source and electronic
components.
The center band pass of the measuring filter is selected to transmit
energy in a narrow region where the component of interest absorbs strongly
in comparison with background absorbance. The center band pass of the
reference filter is selected to transmit energy in a band pass region where the
background absorption of NIR energy is equivalent to that seen by the
measuring filter. The reference filter is also selected to be in a region where
the component of interest has minimal absorption of energy.
The optical beam is converted from steady state to pulsed energy by the
rotation of the filters in the optical path. The measuring and reference pulses
of radiation strike a detector which converts the pulses of radiation into
electrical pulses which are then amplified. Signal processing involves
converting the electrical signals to logarithmic signals, and then comparing
the measuring to the reference logarithmic signals in order to give a readout
representing the concentration of the component of interest in the sample.
1.2 Modules (Condulets)
Physical layout of the analyzer is shown in Figures 1-1 and 1-2. The
control module is usually located apart from the analysis unit in a control
room. The explosion-proof version has the control and analysis units
mounted in one weather-resistant NEMA-12 enclosure suitable for outdoor
installation.
The analysis section is designed for hazardous area installation. Housings are rated for use in Class I, Div. I, Group D hazardous environments.
1–2
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Introduction 1.0
Figure 1-1. Model 514 Photometric Analyzer (with General-Purpose Control Unit)
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1.0 Introduction
Figure 1-2. Model 514 Photometric Analyzer (with Explosion-Proof Control Unit)
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Introduction 1.0
1.2.1 Source Module
The source module or condulet houses the quartz iodine source lamp,
collimating lens/lens holder, and transformer. The 115 VAC power to the
source transformer is derived directly from the line voltage regulating transformer installed in the power module.
1.2.2 Sample Module
The insulated sample module has sample inlet and outlet lines constructed of 1/8" O.D. 316SS tubing. The sample is routed through a
preheater, through the sample cell, then drained from the outlet port. A
thermistor-controlled preheater and compartment space heater are powered
from temperature controllers located in the power module. A thermal cutout
switch prevents temperature “runaway”.
The sample cell, which is configured for each particular application, is
provided with sapphire windows to admit NIR radiation.
1.2.3 Power Module
The power module contains a line voltage regulating transformer (with
capacitor) and three temperature controller circuit cards.
Each of the controllers incorporates a bridge circuit containing a thermistor located in the volume/compartment to be controlled. Bridge imbalance
produces an error signal, resulting in operation of the final control element
(heater) to restore bridge balance, and controlling the temperature to within a
fairly narrow proportional band.
Control functions for the analysis section are located on the power
module (see Figure 4-1).
1.2.4 Detector Module
As noted above, the detector is a part of the optical system (see Figure
2-1). The detector cell is mounted within a hermetically sealed block with a
quartz window through which the optical energy enters. The assembled cell
block, together with the preamplifier subassembly, filter wheel, and filter
position sensor, are contained within a temperature-controlled compartment
In addition to the heated optical compartment, the detector module
contains the chopper motor, power transformer, and six circuit cards whose
function is described in section 2. 2. 4, Detector Module.
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1.0 Introduction
1.2.5 Local Meter Readout
For analyzer configurations having a remotely located control module,
the local meter is used to read the reference and measuring peak heights, or
the voltage output from the buffer amplifier before voltage-to-current conversion.
When the control module is integral with the analysis section, i. e., the
explosion-proof configuration, the meter is connected to the output of the
control module in order to display the concentration of the component of
interest as well as the previously mentioned information.
1.2.6 Control Module
In the explosion-proof version, the calibration meter is used as an all
purpose readout; in this case, there is some modification in the switching at
both the control module and power module.
In addition to control switching, adjustment (zero and span), and readout components, the control module has provisions for five circuit cards: an
automatic zero/extended voltage amplifier, E-to-I converter, I-to-E converter,
power supply, and alarm comparator. The alarm comparator circuit card
incorporates two circuits with jumpers that permit setting the alarm(s) for
high, low, high/low, high/high, and low/low settings. Setpoint adjustments
are performed with potentiometers on the module front panel.
1.3 Typical Applications
WATER MONITORING
Background Typical Range
Acids, including: 0–4000 PPM
Acetic
Formic
Sulfuric
Acetaldehyde 0–1000 PPM
Air 0–2%
Alcohols, including: 0–400 ppm
Butanol
Ethanol
Isopropanol
Methanol
Alkanes, including: 0–500 ppm
Heptane
Hexane
1–6
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Ammonia 0–1000 ppm
Aromatics, including: 0–500 ppm
Benzene
Cumene
Toluene
Xylene
Chlorinated Hydrocarbons including: 0–200 ppm
Carbon Tetrachloride
Ethyl Chloride
Ethylene Dichloride
Methyl Chloride
Perchloroethylene
Propylene Dichloride
Trichloroethylene
Vinyl Chloride
Chloroprene 0–200 ppm
Chloropicrin 0–200 ppm
Deuterium Oxide 0–200 ppm
Epichlorohydrin 0–2000 ppm
Ethylene Glycol 0–500 ppm
Freons 0–500 ppm
Gasoline 0–500 ppm
Hydrogen Fluoride 0–10%
Hydroperoxides 0–5%
Kerosene 0–500 ppm
Ketones 0–1000 ppm
Methyl Acetate 0–1000 ppm
Methyl Methacrylate 0–1000 ppm
Oils 0–1%
Olefins 0–500 ppm
Pentane 0–300 ppm
α-Picolene 0–300 ppm
Phenol 0–1000 ppm
Polyols 0–500 ppm
Propylene Glycol 0–500 ppm
Propylene Oxide 0–200 ppm
Sulfinol 0–15%
Sulfur Dioxide 0–1000 ppm
Vinyl Acetate 0–2%
NOTE: Range may be higher or lower per application.
Introduction 1.0
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1.0 Introduction
OTHER NIR ABSORBERS
Acetic Acid
Alcohols
Amines
Aromatics
Butadiene
Carbonyls
Chloroprene
Esters
Hydrocarbons
Hydrogen Chloride
Hydrogen Fluoride
Hydroxyl Value
Ketones
Olefins
Oximes
Epoxides
Methylene
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Operational Theory 2.0
2.0 Operational Theory
The energy source for the analyzer is provided by a high intensity
quartz iodine lamp located in the source module. Quartz iodine was chosen
because it produces sufficient NIR to operate the system and maintains a
nearly constant brightness over its lifetime. (See Figures 2-1 and 2-2).
This energy is then fed through the sample, which is temperature
controlled, and into the detector module where it passes through a rotating
filter wheel before reaching the lead sulfide (PbS) detector.
The filter wheel, driven at 30 RPS or 1800 RPM by a synchronous
AC motor, contains two optical filters with bandpasses selected for each
application, thus providing reference and measuring pulses from which the
required information may be obtained.
The detector receives pulses at the rate of 60 PPS, or two pulses per
revolution of the filter wheel. Every other pulse is from the measuring
filter, while the alternate pulse is from the reference filter, so that pulses
through the measuring filter alternate with pulses through the reference
filter. A filter position sensor, which is an optical device having an integral
light source and light detector, differentiates between the two.
The two entrained pulses received by the detector each revolution are
amplified through a preamplifier which is physically located inside the
sealed compartment with the filter wheel and detector. This signal is then
sent to a clamping circuit where an exact zero reference is established.
This clamped video signal is then fed through a gain control network,
which is controlled by the automatic gain control loop, through another
amplifier, to the electronic switch. This switch is controlled by the switch
driver network which derives its information from the filter position sensor
in order to separate the entrained video signal into its component parts of a
measuring peak and a reference peak. These peaks are then fed through a
balancing network and channeled into separate peak height detectors which
produce DC voltage levels which are exactly equal to the peak height or
absolute magnitude of the voltage from the base to the peak of each of the
pulses.
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2.0 Operational Theory
At this point the reference signal is fed back to the automatic gain
control loop to maintain the desired system gain. In addition, both the
measuring and reference levels are fed to selector switches in order to
enable direct meter indication, which greatly eases the task of balancing
the system during initial system installation and periods of calibration.
The DC voltage levels are fed to a logarithmic ratio amplifier which
produces a voltage output that is proportional to the logarithm of the ratio
of the two DC input voltages. This output voltage, directly proportional to
the concentration of sample, is, within certain limits, a linear function of
the concentration. For purposes of transmission, the voltage signal is
converted by an E-to-I converter; thus, the output signal from the analysis
unit is a current signal that is proportional to the concentration of sample in
the sample module.
Upon arrival at the control module, which is normally located in a
remote location away from the analyzer unit, the signal is processed
through an I-to-E converter which incorporates fine zero and span controls
for calibration. Following the span control, a buffer amplifier provides
isolation between the calibrated signal and any of the selected output
devices. This signal is then sent to the meter driver circuit and readout
meter, to the alarm comparator circuits, voltage output circuits, current
output circuits, etc., depending upon the particular application requirement.
There is also an option of providing an automatic zero circuit (see
drawing B-14729) in the control unit. This circuit provides electrical
signals for switching a fluid which contains none of the material to be
measured into the sample module, electrically adjusting the zeros and
switching back to sample.
2.1 Circuit Descriptions
2.1.1 Source Module
The source module is the source of infrared energy. This is provided
through the use of a high-intensity quartz iodine lamp operating directly
from a 6.3 V transformer. To ensure a stable source of radiation in the face
of line-voltage variations, the lamp transformer derives its input directly
from a line voltage-regulating transformer, selected for its ability to maintain a constant output voltage level regardless of fluctuations in the input
line voltage within the control range of 105 to 130 VAC.
In some applications where we have an abundance of energy due to
low sample absorption, the focusing lens is removed to avoid excess
energy reaching the detector. However, other systems have high energy
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Operational Theory 2.0
losses in the sample module due to strong sample absorbance or exceptionally long sample path-lengths. These systems require a focusing lens to
gather and collimate the radiation for maximum utilization of source
energy. The collimating lens is quartz.
Figure 2-1. Optical System
2.1.2 Sample Module
The sample cell, generally constructed of 316SS, is located in the path
of the NIR radiation, between the source and the detector modules. Each
compound in the sample path exhibits its own characteristic absorption
spectrum. Cell spacer thicknesses will vary depending upon the absorbance
of the component of interest at the measuring wavelength. Due to the
possible variation of absorption with temperature, it is necessary to maintain the sample at a constant temperature during analysis. To achieve this,
two separate methods of temperature control are employed
1. A preheater is used on the incoming sample stream to raise it to
the desired level.
2. The entire sample module is separately controlled to maintain
the sample temperature during analysis.
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2.0 Operational Theory
Figure 2-2 Analyzer System - Block Diagram
2.1.3 Power Module
See Figure 2-3. The power module controls power to the analyzer unit,
providing the switching function for the local meter, and providing temperature control for the sample and detector modules. In the case of the explosion-proof configuration, where the control unit is mounted locally, the
power module simply routes the AC input power to its destination and
allows the control unit to provide the ON/OFF function.
When power is applied to the system, it is directed to the constant
voltage transformer and to the three temperature controllers which are
insensitive to line voltage fluctuations.
In order to facilitate easier calibration and to provide a quick visual
indication of the instrument’s status, a local meter is provided. With the
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Operational Theory 2.0
NORM/ZERO switch on the power module set to the NORM position, the
meter will provide a constant readout of either the reference level or the
measuring level. During calibration periods, the ZERO switch control may
be used to monitor the signal into the E-to-I converter, and if a known zero
sample is applied, then the ZERO potentiometer may be varied to ensure
zero output to the control unit.
115 VAC
60 Hz
Input
S1
From Detector Module
Power
15 VDC
MEAS
REF
ZERO
5A
Coarse
Zero
Control
Selector
Switch
Line Voltage
Regulator
Transformer
To Log Amplifier
To Meter Driver
Preheater
Temp.
Control
Sample
Module
Temp.
Control
115 VAC to
Source Module
115 VAC to
Detector Module
Thermistor
and Heater
Thermistor
and Heater
Detector
Module
Temp.
Control
Thermistor
and Heater
Figure 2-3. Power Module - Block Diagram
All of the temperature controller circuit cards for the analyzer are
located in the power module. The schematic diagram for these circuits is
shown in dwg. B-15016.
The purpose of the time-proportional temperature controllers is to sense
the temperature in the compartment or volume to be controlled and, at a rate
of approximately twice per second, turn on the heater(s) for a specified
portion of the time cycle, depending upon how much heat is needed. When
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2.0 Operational Theory
ON, the heater is fully turned on; only the duration of the ON interval will
vary.
As the compartment heats up, the heater-on time interval is shortened.
The less heat needed, the shorter the heater-on interval during each cycle.
Since TRIAC Q1 is used as the control element for the heater, it is supplied
with the full AC line power. The output TRIAC is mounted on a heat sink
and can handle the full heater wattage.
A4 is a zero crossing switch and TRIAC driver, providing a gating
signal output pulse to turn on the TRIAC. Turn-on pulses are only applied
to TRIAC Q1 when commanded by a control signal, i.e., at the time the
line voltage crosses zero.
A1B is a comparator that compares the output of the temperature
amplifier (voltage representing temperature) A1A (at pin 5) with a reference ramp voltage from A2B (at pin 6), causing TRIAC Q1 to be turned on
for a time interval proportional to the required heat.
A2B and A3 comprise a ramp generator that produces a sawtooth
voltage ranging from 6 to 12 VDC with a period of approximately one-half
second.
The output voltage from the temperature amplifier A1A will range
from less than 6 volts to something more than 12 volts. When the output
voltage is greater than 12 volts, the TRIAC will be turned on a full time
interval each cycle. When the output is less than 6 volts, the TRIAC will be
turned off all the time. When the output is in the middle of the range
(approximately 9 volts), the TRIAC will be turned on for about one-half of
the time interval.
The thermistor, which is a negative temperature coefficient device, is
set up in a bridge circuit. Resistor R2, the setpoint resistor, is selected to be
approximately equal to the resistance of the thermistor at the desired
operating temperature. The other half of the bridge, the voltage divider
network comprised of resistors R4 and R5, is balanced. When the resistance of the thermistor is equal to the resistance of R2 at the desired operating temperature, the bridge is balanced and the voltage at pins 2 and 3 of
A1A is the same.
When the temperature in the compartment rises, the thermistor resistance will decrease and the inverting input of A1A will fall below the
reference point. This input will be amplified by A1B to broaden the proportional band and preclude the possibility of the device overshooting and
operating as an on/off temperature controller.
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To
Power
Module
PbS
Detector
Circuit components C1, D3, and D4 provide stable internal power to
the rest of the controller circuitry.
Video
Signal
Preamplifier
Filter
Position
Sensor
Heater
&
Therm.
Detector
Compartment
Power
Supply
Filter Pos.
Signal
(Gate Pulse)
15 VDC
24 VDC
Clamp
Signal
Switch
Driver
Timing
Clamped
Video
Clamping
Switch
Operational Theory 2.0
Manual Peak Balance
Video
AGC
(+9VDC)
Ref.Level
Ref. Level
Switching Signals
(S, S', P, P')
Log
Amplifier
0to0.4VDC
FullScale
Elec.S ig.
Sw. & Peak
Level Detect.
Meas.Level
(+9VDC)
Coarse
Zero
Control
From
Power
Module
To Meter
115 VAC
60 Hz
Input
Power
Transformer
Chopper
Motor
E-to-I
Converter
Com.
10 to 18 mA (Nominal Value)
To ControlModule
Figure 2-4. Detector Module - Block Diagram
Operating controls for the analysis section are located on the door
casting of the power module enclosure. In the general purpose configuration, these controls include the POWER ON/OFF switch, the MEAS/REF
switch to select the measuring or reference peak voltage to be fed to the
local meter driver, ZERO control, and the NORM/ZERO switch, which
operates in conjunction with the MEAS/REF and ZERO controls.
When used with the explosion-proof control module, the NORM/REF
and NORM/MEAS switches are used on the module instead of the MEAS/
REF switch. A NORM/ZERO switch is also included.
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2.0 Operational Theory
2.1.4 Detector Module
See Figure 2-4. After energy has passed through the sample, it arrives at
the filter wheel where it is fed alternately through two filters (measuring and
reference) before reaching the detector.
These filters are specially selected for each application according to the
absorption characteristics of the compounds under analysis. The reference
and measuring filter waveforms occur along a baseline at approximately 16
milliseconds intervals; each reference or measuring waveform reoccurs at a
time interval of 33 mS, or one per revolution of the filter wheel.
At the detector, infrared energy is transformed into electrical pulses and
fed through an impedance-matched preamplifier (see dwg. A-14619). Depending upon the application, length of the cell spacer, etc., the gain of the
preamplifier may vary from 1 to 10, depending upon the energy intensity at
the detector, to achieve an AC signal output of approximately 0.1 to 1.0 volt
peak-to-peak.
Additionally, the detector, filters, and preamplifier are housed in an
electrically and thermally isolated box to provide maximum stability and
minimum noise. This box, or compartment, is normally temperature controlled at 46 °C.
The negative-going video from the preamplifier is fed to the clamp
circuit (see dwg. B-14561) to establish a precise zero reference to the
baseline of the pulses. This is accomplished by applying a gate to Ql at a
time when neither filter is in the energy path. This gated signal is fed
through A2 where it subtracts itself from the composite signal at the noninverting input. The signal output of A3 is clamped to ground and has an
amplitude of approximately two times the input.
The gating pulse for the clamp circuit is derived from the filter position sensor which is located in the detector compartment. The sensor emits
radiation which is reflected from the white pattern on the rear side of the
rotating filter wheel and sensed by a photo transistor. This creates a square
wave of 5 volts amplitude at TP4 which is then further processed by Q2,
A4 and A5 to generate the gating pulse for the clamp circuit as well as the
switching signals S, S', P and P', which are later used to demodulate the
composite video.
The clamped-to-ground, negative-going video is then sent to the
automatic gain control circuit (see dwg. B-14564). This circuit receives a
reference signal from the peak level detector and uses it to adjust the
current through LEDs B1 and B2. The current through LED B1 controls its
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Operational Theory 2.0
light output and, therefore, the resistance of its shunt resistors. This enables
the signal at TP2 to be continually adjusted up or down to hold the reference
signal at a constant level (nominally 9 volts) and thus eliminate the effects of
turbidity or other foreign substances in the sample, within design limits.
After the automatic gain control circuit, the signal proceeds to the peak
level detector, where it is demodulated by A1 and A2, using the timing
signals previously generated (see dwg. B-14554). Potentiometer R3 can be
used to precisely balance the signal levels by adjusting the feedback loop
gain resistance of the two respective peaks. The separate peaks are then sent
through peak detector networks where they are transformed into stable DC
voltage levels. In the case of the reference peak level, it is from here that a +9
VDC signal is fed back to the automatic gain control network. The signal
levels are then fed to either one of two logarithmic ratio amplifiers (see dwgs.
C-14586 and C-14907).
For applications of high sensitivity, a chopper-stabilized log amplifier is
used (see dwgs. C-14586 and C-17706). A3 generates an approximate 200
Hz square wave which alternately allows the signals to be fed into the log
amplifier (A1) itself, and then blocks the measuring level and feeds the
reference level into both log amplifier inputs, allowing it to zero itself. The
log signal is then applied through amplifier A4 and A6 to A7 where a
coarse zero offset voltage may be applied through the ZERO potentiometer
on the power module
For less sensitive applications, a simpler log ratio circuit is used (dwg.
C-14907). The reference and measuring levels are processed through a
filter network before being compared by A1. This comparison results in
the log ratio output which is fed to A2 for application to a zero offset
voltage from the zero adjust potentiometer on the power module.
From the log amplifier the signal is finally sent to the voltage-tocurrent (E-to-I) converter for transmission to the control unit. Conversion
of the voltage signal to a current signal allows for signal transmission over
greater distances without noise pickup.
The E-to-I converter (see dwg. B-14075) is set with a nominal offset
so that with 0 VDC input, 10 mA output is obtained. This baseline setting
is adjustable through R7, the zero adjustment.
The converter is scaled so that with a 0.5 VDC input, the output will
be 20 mA (set with balance potentiometer R12). Output nominally ranges
from 10 mA to 18 mA with a 0 to 0.4 VDC input. When required, zero
drift can be accommodated; i.e., inputs ranging from -0.5 to +0.5 VDC will
produce 0 to 20 mA outputs.
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies
2–9
2.0 Operational Theory
Power for the detector module is provided by a center-tapped transformer which takes 115 VAC input, reduces it to 40 VAC, then feeds the
voltage to the DC power supply. An additional winding on the transformer
provides output power to the E-to-I card.
The power supply utilizes a fullwave rectifier in order to provide +24
VDC unregulated. The 24 VDC is further filtered, then fed through a
voltage regulator to obtain +15 VDC regulated.
As noted previously, the filter wheel is driven by a synchronous AC
chopper motor which operates at 1800 RPM. The filter wheel performs
two functions: (1) switching filters, and (2) chopping the optical signal to
give pulses which can be amplified for high quality processing.
2.1.5 Control Module
The control module provides voltage and current output signals which
are properly scaled for the application, alarm signals in the form of relay
contacts, and a meter output. Optional provisions are also included for an
automatic zero and dual-range capability.
Upon arrival at the control module, the milliampere signal is converted to a 0 to +2 volt full scale output for connection to the span
potentiometer (see dwg. A-14620). An optional millivolt output can also be
provided by the I-to-E converter circuit card. At this point, fine zero
control is also applied by means of a potentiometer located on the front of
the module.
The voltage is then scaled so that 1 VDC full scale output is obtained
at the center of the span potentiometer. This signal is coupled through an
extended voltage amplifier circuit and used to drive the 0 to 100 µA meter
on the control module.
The standard 0 to 1 VDC output is also generated by the extended
voltage amplifier circuit (see dwg. B-16221).
The 0 to 1 VDC full scale from the span potentiometer is connected to
the alarm comparator circuit (see dwg. B-14718) where it is used to drive a
pair of amplifier circuits which couple the alarm setpoints to relays K1 and
K2.
A current output (normally 4 to 20 mA) is optional. If desired, an
optically isolated current transmitter can be installed in the explosion-proof
control module.
2–10
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies
Operational Theory 2.0
Power for the control module is provided by a center-tapped transformer which takes the 115 VAC input, reduces it to 40 VAC, and feeds the
voltage to a DC power supply identical to the one installed in the detector
module. Power supply outputs are +24 VDC unregulated, and +15 VDC
regulated.
To Timer
Power
115 VAC
60 Hz
Input
Current
Signal
Input
From
Analysis
Unit
Power
Supply
Power
Transformer
Manual
Fine Zero
I-to-E
Converter
115 VAC
60 Hz
±
15 VDC
24 VDC
±
To I-to-E Converter
Span
Adjust.
Ext. Volt.
Auto
Zero
Timer
Amplifier
Meter
Indication
(0 to 1 V f.s.)
(0 to 5 mV f.s.)
Manual Setpoint Adjust.
Voltage
Millivolts
#1
Comparator
#2
Alarm
Relays
Output
N.O.
N.C.
N.O.
N.C.
Com.
Com.
E-to-I
Converter
(4 to 20 mA)
Figure 2-5. Control Module - Block Diagram
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies
Current
Standard
Valve
Control
Signal
2–11
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