Powder dosing - Lambda
INSTALLATION OF DOSER

1. SETTING UP THE POWDER DOSER

1.1 Pre-treatment of the solids

Solids have to be homogenous and free flowing. If this is not the case, they should be recrystallized, dried and sieved to remove the fines.

The free flow of difficult solids can be achieved by the addition of AEROSIL 200 or 974 at a concentration of 0.1 to 2 %. AEROSIL is super finely dispersed pure SiO2. Its particles cover the surface of the crystals and make it free flowing. AEROSIL is non-toxic, chemically inert and can be removed by filtration. It can be obtained at a low price from us or from DEGUSSA AG, Oberdorfstrasse 11, CH-6340 Baar.

1.2 Assembly of the LAMBDA DOSER

The setup of the LAMBDA DOSER is very easy:

• 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 centre 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 a 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.

1.3 ON/OFF button

By pressing the ON/OFF button the powder dosing instrument is switched on or off. The internal memory will show the last used speed and flow direction setting.

1.4 Setting of the dosing speed

The powder dosing rates depend on the powder properties and the DOSER motor rotation speed.

The speed of powder addition is selected by the control buttons Λ Λ Λ under the LED display. The digital selection allows for good reproducibility of the selected dosing rate.

Since specific densities of solid substances vary considerably, it is important to calibrate the DOSER before starting the powder dosing. For this, the amount of substance delivered during a certain time period is measured (e.g. for 1 minute with speed setting 500). The speed of rotation of the distributor increases progressively with the speed setting value. Using this information the speed setting corresponding to the desired flow rate of the solid substance can be calculated easily (rule of three).

The dosing of the powdery substance is started by pressing the ON/OFF button. The corresponding LED indicates that powder dosing is in progress.

1.5 Use of the DOSER during reflux or under controlled atmosphere

Vapours of boiling solvents can penetrate into the lower part of the DOSER and condense. The 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 vapours are displaced and cannot disturb the dosing.

The gas is introduced by a special stopper fitted with tubing. For this purpose we deliver a polyethylene stopper. However, any fitting compatible with NS 29/32 ground fittings (e.g. SVL threaded fittings which can be adapted to several tubing diameters are excellent). The slight gas stream 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 the dosing process.

Since the DOSER is airtight, it can also be used for work under controlled atmosphere (nitrogen, argon etc). The DOSER withstands a pressure of ± 0.05 MPa. The airtight DOSER is particularly useful during work with oxygen sensitive or hygroscopic substances. In this case manual dosing is very difficult.

2. PROGRAMMING OF THE DOSER

Up to 30 pairs of time and speed settings (flow rates) may be programmed in a simple way. The programming mode is accessed by simultaneously pressing the buttons REMOTE and RUN until the indication “PGM” appears on display and the REMOTE and RUN LEDs are switched on.

Remark: If you repeat this simultaneous pressing of the REMOTE and RUN buttons, the memory will be cleared and the indication “cLE” will appear on the display. To enter the programming mode again, press the REMOTE and RUN buttons again until “PGM” appears.

• Press the ON/OFF button. The indication “F01” will appear for a short time on the display indicating that you can select the first flow rate (speed setting) value.

• Set the desired flow rate value for the first program step by pressing the buttons Λ Λ Λ below the display (from 0 to 999, corresponding to 0 to 100% of the motor rotation speed).

• Press the ON/OFF button. The indication “t01” will appear for a few seconds on the display indicating that you can program the time period of the first step in minutes. Select the desired time period for the first program step by pressing the buttons Λ Λ Λ below the display (from 0 to 999 minutes).

• Press the ON/OFF button. The indication “F02” will briefly appear on the display. You can now enter the desired flow rate for the second program step. After this press the ON/OFF button again. The symbol “t02” will briefly appear on the display. You can now set the time of the second program step.

• In a similar way up to 30 program steps can be entered.

• After having entered the time of the last step, press the ON/OFF button. The flow rate (000) of the next step which will not be programmed appears on the display. Press both REMOTE and RUN buttons simultaneously until the indication “End” appears on the display. The REMOTE and RUN LEDs will be switched off.

After the last program step the DOSER will continue dosing with the speed setting of the last program step until it is switched off manually. If you wish to stop the dosing after the last step program an additional step with flow rate 000 during for example one minute. Then press the REMOTE and RUN buttons to exit the programming mode.

Remark: It is not possible to end the program after programming the time data.

To start the program, press the RUN button. The RUN and ON/OFF LEDs are on.

To stop the running program definitively, press the RUN button. The RUN and ON/OFF LEDs are off.

It is possible to stop the pump by pressing the ON/OFF button, to change the rotation speed during any running program step. This allows reaction in emergency situations.

Remark: Do not forget to switch the powder doser on again (by pressing the ON/OFF button) after you have finished your intervention.

The time basis in the microprocessor is not stopped during this intervention, so that the total time of the running steps and of the whole program will not be affected. When the program step time has elapsed, the DOSER will automatically go on with the next program step. Thus, the program is not modified by this emergency intervention.

It is possible to review the program by proceeding in the same way as during programming but without modifying it.

3. REMOTE CONTROLS

3.1 ON/OFF remote control

By interlinking the contacts no. 4 and 5 of the socket at the rear of the pump (see fig. 5 and section 7.2), the powder dosing instrument will be blocked and the ON/OFF LED is off.

The same effect will be obtained by applying a voltage of 3 to 12 V DC to the contact no. 5 (0 line must be connected to contact no. 3). The remote control cable (Art. no. 4810) is used for the transmission of the remote control signals.

Remark: In some cases a reversed logic for the remote control might be desired. Please contact us in this case.

3.2 Remote control of the dosing speed

The LAMBDA DOSER powder dosing instrument can be controlled over the whole speed range by an external signal (0 - 10 V DC, option 0-20 or 4-20 mA). The plus pole of the signal is connected to the contact no.1, 0 line to the contact no.3.

Press the button REMOTE on the front panel. The corresponding LED diode will go on and the display will indicate the approximate voltage of the external signal. This indication may become unstable when no external connection is made and indicates the high sensitivity of the electronics.

! For safety reasons the voltage of the external signal must not exceed 48 V to earth!

3.3 PC control

When the instrument has been equipped with the optional RS-232 or RS-485 interface, it can be controlled digitally, e.g. from a PC.

The address of the instrument is set by pressing the button ADRS. The message “A” and two numbers will appear on the display. This number from 00 to 99 is the current address of the pump. To change the address press the buttons Λ Λ Λ under the display until the desired number is obtained. To confirm the address and save it, press the ON/OFF button.

4. CLEANING THE DOSER

After use, the motor unit is pulled out of the DOSER head until both separate. (Do not be afraid to pull hard, as the blocking mechanism requires it). Loosen both threaded caps and separate all components inside the tube. The parts can now be washed by common laboratory methods (for example with ethanol, acetone, diluted acids or bases). It is however not recommended to expose parts to these reagents for long periods of time.

The motor and control unit can be cleaned only with a piece of cloth soaked in water containing a mild detergent, diluted ethanol or with more care iso-propanol. Use of other solvents could damage the surface of the unit.

If you have any difficulties or questions concerning your DOSER powder dosing instrument, please contact our service office.

5. FOR YOUR SAFETY

Thanks to the use of a plug-in power supply giving only a low voltage of 12 V DC the danger of electrical shock during the use of the DOSER powder dosing instrument has been virtually eliminated, even when an electro conductive solution penetrates the DOSER.

If the dosing pump is not used for an extended period of time, disconnect it from the mains. A modern miniaturized switching power supply is used, which has only a negligible consumption of electric current when the powder doser is not in use.