How to put the Lambda Doser together
The preparation of the doser for use is very easy.
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The ground glass piece (b) is put through the threaded cap (a) (figure 1).
The teflon disc (c) is put inside the cap and placed on the ground surface of piece (b) and the cap is screwed to the glass tube (d).
- The distributor (e) is put inside the glass tube with its opening directed downwards so that it will not be damaged (figure 2).
- There is a silicon baffle on the lowest part of the tube. The distributor must be turned with its opening towards this baffle.
- The teflon treated rubber seal is placed on the head (f) with the teflon layer facing outside (towards the glass tube). Put the axis of the distributor through the center of the head (figure 3) and tighten it with the threaded cap (a) to the glass tube.
- Press the axis of the motor unit completely inside the head so that the metal pin will fit into one of the six corresponding holes in the head (figure 4). This assures a perfect seal of the doser and sufficient pressure of the distributor against the teflon disc in the bottom of the doser tube.
- By loosening the upper threaded cap you can put the filling tube into the desired position then tighten the cap again.
- The solid is added through the filling arm of the tube. The filling arm can be closed with a ground glass or plastic stopper NS 29/32.
- The 12 V connector of the power supply is plugged into the 12 V DC socket of the motor unit (figure 5) and the power supply is connected to the mains.
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SELECTION OF THE DOSING SPEED
The speed of addition is selected by three decimal switches "speed control". The digital selection allows good reproducibility of the selected flow.
Since specific densities of solid substance vary considerably it is important to calibrate the doser before starting work. The amount of substance delivered during a certain time period is measured. The speed of rotation of the distributor increases progressively with the "speed control" value, therefore it is possible to calculate the "speed control" adjustment corresponding to the desired flow rate of the substance.
The delivery of a solid starts by switching the rocker switch to position "I". The green light of the diode indicates that the dosing is in progress.
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USE OF DOSER DURING REFLUX OR UNDER
CONTROLLED ATMOSPHERE
Vapors of boiling solvents can penetrate into the lower part of the doser andcondense.
This condensation disturbs the flow of the solid. This can be prevented by blowing a light stream of air or another convenient gas through the doser tube. The vapors are displaced and cannot disturb the dosing.
The gas is introduced by a special stopper fitted with a tubing. For this purpose we deliver a polyethylene stopper. However any fitting compatible with NS 29/32 ground fittings (eg. SVL threaded fittings which can be adapted to several tubing diameters are excellent). The slight stream of gas passes through the hollow axis of the distributor and the lower part of the doser tube. The stream and pressure of the gas must be carefully controlled to prevent compression of the solid substance during dosing.
Since the doser is airtight, it can also be utilised for work under controlled atmosphere (nitrogen, argon etc). The doser withstands a pressure of +/- 0.05 mPa. The air-tight doser is especially usefull during work with oxygen sensitive or hygroscopic substances. In this case manual dosing is particularly difficult.
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REMOTE CONTROL
Remote control on/off
By interlinking the contacts no. 4 and 5 of the socket on the rear of the pump (see figure 5 and 6) the motor will be blocked. The same effect will be obtained if you apply 12 V to the contact no. 5 (0 V line is connected to contact no. 3) (figure 5 and 6). The remote control
cables (cat. no. 4804 or 4810) are used for transmission of remote control signals.
Sometimes a reversed logic for the remote control is required. This can be obtained through
switches S2 and S3 on the circuit board (see section 7).
Remote control of the speed
The speed of rotation can be controlled over the whole range by an externalsignal (0Ú1 V) when applied to the contact no. 4 of the socket "remote controle" on the rear of the motor unit (figure 5 and 6) and when the neutral conductor is connected to the contact no. 1 the "speed control" switches must be switched to "000".
! Attention: for safety reasons the voltage of the external signal must not exceed 48 V to earth.
Control by line voltage
The doser can be controlled by switching the mains on and off *. This type of control can be used with scontrol instruments (eg. pH, temperature, etc.) with outputs of 230 V. In this case there will be a certain inertia of the doser when switching on and off. This can be completely eliminated by using our adaptor (Cat. no. 4804) which simultaneously allows the connection to our Pump-Flow Integrator (Cat. no. 4803).
* This does not damage the doser.
Note: When the doser is switched off by remote control, the green light of the diode changes to yellow.
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