CD 3002 Sensor Manual
Your eye in hell
© Siemens Laser Analytics AB Oct 2001 CD 3002 Sensor manual Document number: CID 3002-1102 Rev. 2A
LDS 3000 Sensor manual
Content
Content 1. CD 3002 1.1 General 1.2 Protecting the optical surface
2. Installing and aligning CD 3002 2.1 Mechanical installation 2.2 Connections
3. Maintenance 3.1 Cleaning of lenses
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Content
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LDS 3000 Sensor manual
LDS 3000 Sensor manual
CD 3002
1. CD 3002 1.1 General The cross duct sensor, CD 3002 (a sensor for measuring through a gas channel) is designed for in-situ measurements. It consists of a transmitter and receiver creating a single path measurement situation. The beam diameter is expanded to about 2 cm in order to improve performance in high dust load (>1 g/m3) applications.
Process flange
Lens
Quick connect Fiber optic connector EMC proof cabinet
Component parts of the CD 3002 sensor (transmitter side).
The transmitter includes a lens and a connection for the optical fibre located in the focal plane of the lens. The receiver contains a lens, a detector with preamplifier, driver electronics for the optical return signal, and a 24 VDC to ±15 VDC DC/DC-converter. The laser light is coupled from the optical fibre in the transmitter to the transmitter lens and passes through the measurement volume. The lens in the receiver focuses the incoming laser light on the detector where it is converted to an electrical signal. This signal is amplified and converted to an optical signal and returned to the central unit CU 3000. The mounting of the sensor requires a DIN-flange with the dimensions DN65/PN6. Other flange dimensions are available as options.
1.2 Protecting the optical surface The lenses are in many applications exposed to very nasty environments and will get stained very quickly if no measures are taken. There are a number of methods available to keep the lenses in good shape. They will all be described here but the method used in your particular application will be found in the application section of this manual.
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LDS 3000 Sensor manual
CD 3002 Instrument air purging
This is the standard solution to keep the lenses free from contamination. It requires a flange equipped with an inlet for purging gas to create an air flow in front of the lenses and into the process. Before entering the process the air is passed through a steel filter to create a laminar flow away from the lens into the process. This prevents backward going jet streams from building up. The Cv for this filter is 0,39 giving a flow of approximately 500 ltr/min. if 6 bars is applied directly on the filter (bypassing any flow reduction). The purging gas outlet should therefore be pressure regulated near each sensor unit. As an option a needle valve can be used instead to give an adjustable air flow of approx. 20- 120 ltr/min. (with 6 bar instrument air).
Air buffer
Sintered steel filter (gives laminar air flow)
Instrument air inlet
Set-up for purging the lens with 6 bar instrument air
Instrument air is rather expensive and therefore measures should be taken to minimize the consumption. Therefore a pressure regulator should be used at the instrument air connection point to facilitate adjustment of the flow if no flow regulation is applied. If very high air flows (>100 ltr/min.) are needed an air blower should be used.
Flow calculations Gas flow calculations are slightly complex because gases are compressible fluids whose density changes with pressure. In addition, when outlet pressure is less than one half of the inlet pressure, the gas reaches sonic velocity in the valve. This is known as “choked flow”, because a further decrease in outlet pressure does not increase the flow. In this application we are dealing with choked flow. The following equation can be used to calculate the flow under these circumstances: 1 q = 3271 ⋅ C v ⋅ p 1 ⋅ ---------------T1 ⋅ Gg where q = flow rate on low pressure side [Nltr/min.]
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Note!
LDS 3000 Sensor manual Cv = p1 = Gg = T1 =
CD 3002
flow coefficient (0,39 for our standard sensor) inlet absolute pressure [bar] gas specific gravity (air = 1.0) absolute upstream temperature [K]
The flow (q) of instrument air at p1 = 2 bar and T1 = 25 °C through the steel filter would then be ~150 Nltr/min.
Heated instrument air purging In some applications, like in waste incineration, where a large number of reactive gas components are present the purging air must be heated to prevent condensation of salts on the lens surface. To do this the optional air heater AH 3000 can be used. It uses a 2 kW heating element and can be set to heat the air up to 250 °C at a maximum air flow of 500 ltr/min.
Purging with air blower In applications with high dust load purging with air blower must be considered. The air speed when standard purging is used is too low to prevent build-up of dust in the flange tubes. Our standard fan solution will provide up to 1000 ltr/min.
Air buffer
Hoose to air blower (gives ~1000 ltr/min) Set-up for purging the lens with a fan
Steam purging If overheated steam is available it is a candidate for purging of the lenses. It has some advantages like high temperature (to prevent salt condensation) and low maintenance. An additional advantage when oxygen is measured is that steam is free of oxygen and will not interfere with the measurements. Consequently when water is measured this becomes a disadvantage. When oxygen is measured N2 purging of the sensor housing might also be necessary to obtain maximum performance.
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CD 3002
The requirements on the steam is that it must be ~200 °C and overheated at the sensor location. Se the steam installation instruction provided by Siemens Laser Analytics AB.
Air buffer
Tubing for the steam i.e. 6 mm steel tubes Setup for purging the lens with steam
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Installing and aligning CD 3002
2. Installing and aligning CD 3002 The installation of CD 3002 is very straightforward and can be performed by the customer.
2.1 Mechanical installation The transmitter and the receiver of CD 3002 requires a process flange of dimensions DN65/PN6. Additionally, depending on application, one or two of the following might be needed a) a supply of instrument air with 2-6 bar pressure regulation b) 200 °C - 4 bar steam c) electrical power for a 1 phase 2 kW (connected power) heater or d) electrical power for 500 W 1 phase electrical motor. The instrument air is the most common way of keeping the lenses clean and should be connected using 6 mm (outer diameter) semi-rigid tubing.
00 mm
~150 – 4
Purging gas tube with an outer diameter of 6 mm 4
∅1
∅6
5
30 ∅1
0
∅16
DN65/PN6 Flange dimensions
Note!
The process flanges must be mounted parallel to each other and the maximum error angle is ±2 deg relative to the symmetrical axis of the two flanges (transmitter and receiver)
At installation of CD 3002, the fiber end and the photo-detector have to be aligned to the optical axis of the sensor pair. A complication is that
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LDS 3000 Sensor manual
each lens has an optical axis of its own which is its axis of symmetry. Normally the process flanges are mounted with an angle error. CD 3002 is, however, equipped with a flange pair with a spherical interface. This is used when the sensor pair is aligned to each other (the alignement procedure is described on the next side). This way an angle error of up to ±2° on each side can be adjusted for, see figure below.
max 2˚
Sensor alignement flange
The stability of the sensor alignement depends on the stability of the construction to which the customer flange is mounted. If the incinerator wall or smoke duct is subject to movements due to for instance thermal changes CD 3002 will need repeated realignment. This can be avoided by mounting the sensor pair on an external, more stable base, like a concrete or steel incinerator support.
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LDS 3000 Sensor manual
Installing and aligning CD 3002
The sensor is aligned using the sensor alignment kit AK 3002. The aligning procedure is as follows:
Receiver side 1. Start by aligning the transmitter side. This is done by removing the receiver at the quick connect interface and instead mount the Ø100 mm alignment flange. Here the alignment lamp is mounted and defines the optical axis of the sensor pair. Check that the lens is clean on the receiver and that the purging is working while it is dismounted.
Alignement lamp
Alignement flange
Receiver side
Note! Note! Note!
Sometimes the visibility in the measurement path is poor. The reason for this might be high dust load, smoke or strong ambient light from the process (as in a combustion chamber). In this case a stronger light source must be used in the first alignement step. Siemens Laser Analytics can supply a suitable light source labelled HL 3000. In the case of very strong ambient light in the measurement volume it is sometimes possible to align against the black dot originating from the hole in the flange on the opposite side. If the process pressure is above ambient it can be dangerous to dismount the sensors. Even if the pressure conditions normally are below ambient pressure variations can result in “blow-out” of hot gases from open flanges. Please consult plant personal before starting the alignement procedure.
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LDS 3000 Sensor manual
Transmitter side 2. Dismount the transmitter and check that the lens is clean on the transmitter and that the purging is working. Then mount the transmitter and twist-dismount the launcher (fibercable connector in the middle), twist-mount the cross hair instead. Align with the four alignement screws on the flange, the light dot must be centred in the inner ring of the cross hair.
Alignement screws
Cross hair
Transmitter side
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LDS 3000 Sensor manual
Installing and aligning CD 3002
Transmitter side 3. Twist-mount the alignement lamp instead of the cross hair in the transmitter.
Alignement lamp Transmitter side
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Installing and aligning CD 3002
LDS 3000 Sensor manual
Receiver side 4. Mount the receiver back again and twist-mount the cross hair instead of the detector module. Align with the four alignement screws on the flange, the light dot must be centred in the inner ring of the cross hair.
Alignement screws
Cross hair
Receiver side
CD 3002 is now aligned and the holder for the fibre connector and the detector module should be mounted in their places. Finally, instrument air, or which ever method is used to protect the optical surfaces, should be connected to the appropriate inlets both at the transmitter and receiver side of the sensor. The mechanical stability of the sensor mechanics is sufficient to allow dismounting (the quick connection) of both the receiver and the transmitter. This means that cleaning of the lenses does not require re-alignment of the sensor.
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Installing and aligning CD 3002
2.2 Connections All electrical connections are made in the receiver. The hybrid cable is connected to the transmitter where the return fibre and the pair wire are continuing to the receiver in the loop cable. The connections are illustrated below.
Receiver
Transmitter
Return fiber
Transmitter fiber Launcher
24VDC DC/DC card
Detector cable
Loop cable ±15 VDC
Hybride cable
Sensor card
Detector card
Connections
Five test points are available on the sensor card. Here the power and signal levels can be examined using an oscilloscope or a multi-meter. At installation, the signal levels should be adjusted to be between 2 and 4 volts peak. This is done with the two potentiometers on the detector card and sensor card respectively. The potentiometers are factory-adjusted to minimum gain. Trained installation personal are allowed to set proper gain level for the application. The detector card is mounted in the detector housing, see figure below.
Potentiometer
Detector housing
The sensor card is shown below.
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Level potentiometer
+V Signal GND –V Signal + GND
Detector module connection
Installing and aligning CD 3002
±15 VDC input Return LED
Test points Sensor card
The powering of the receiver electronics is performed with a twisted pair copper cable delivering 24 VDC. This voltage feeds a DC/DC converter able to give ±15 VDC and to handle 18 to 36 VDC on its input. This means that the system can handle large variations on the sensor voltage and thus will be very resistant to disturbances. The DC/DC card is shown below.
– 0 +
– +
24 VDC input
±15 VDC output
DC/DC card
In some systems the DC/DC card and the sensor card are combined to one card. On these cards the level potentiometer is removed as well leaving the potentiometer on the detector card as the only adjustment point in the sensor. This card is shown in the next picture.
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Installing and aligning CD 3002
Detector module connection Test points
Return LED 1 2
24 VDC input
7 8 1. -12V 2. Signal 3. PE GND 4. +12V 5. GND 6. GND 7. GND 8. GND
Sensor card and DC/DC card combined
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Installing and aligning CD 3002
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Maintenance
3. Maintenance Normally the only maintenance needed for LDS 3000 is to clean the optical surfaces facing in to the measuring volume. In some occasions a realignement of the sensor pair might be necessary.
3.1 Cleaning of lenses Before the sensors are removed make sure that: • if there is steam purging – it’s turned off.
Note!
It is very important to turn off the steam since over-heated steam is invisible and can cause severe burn damages.
• no hazardous or hot gases can escape from the process. • appropriate protection against hot surfaces on and around the sensor is used. Remove the quick connect – no tools are needed – and pull the sensor out. In some installations a wedge module is used and if so, this module should also be removed. If the optical lens needs cleaning extra care should be taken since it is anti-reflection coated and sensitive to scratches Remove all particles using pressurized air or flushing water. Clean the optical surface with a soft cloth or window cleaner containing ammonia. Soap water also works fine in many cases. Start at the centre and work with circular movements towards the rim. When the sensor is re-installed make sure that the guide pin fits the hole on the lens tube. Mount the quick connect and tighten it by hand, This operation does not affect the sensor alignement if properly performed.
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Maintenance
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