With integrated flow meter and monitoring

Micro-capacity diaphragm dosing pump

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Dosing pump technology has developed to keep pace with the new needs of the market in the area of micro-dosing. The new generation of dosing pumps combines the latest drive technology with a high-performance micro-controller. In the near future, according to the manufacturer, stepping motor-operated dosing pumps with an integrated flow meter and setpoint control will become the state of the art.

Mehdi Ayatollahzadeh

The use of diaphragm dosing pumps with very low capacities of no more than 20 l/h is growing all the time, particularly in water technology and industrial process engineering for disinfection and treatment. Precision micro-dosing is also becoming more important in cleaning and defoaming applications as well as in other sector-specific processes. Highly concentrated chemicals are increasingly used as dosing media – and not just for reasons of economy in transportation and storage.
When developing this dosing pump, the manufacturer had to ensure functionality and precision at levels which would have been unthinkable in the past. In addition, the use of different dosing media with different physical and chemical properties such as outgassing or viscosity had to be facilitated.
Since complex process-specific adjustments require a large amount of operator input, it was also necessary to make the new devices much easier to operate.
Users moreover wanted reliable control of the dosing process and simple, unproblematic analogue or digital communication. And of course all these high-tech features needed to be offered at prices which would still be attractive to the customer.
Technical solution
Until recently, low-capacity dosing pumps were mainly operated by a solenoid drive or a synchronous motor. The dosing rate was set manually by altering the length of the stroke. With low dosing rates or when dosing outgassing media, mechanical stroke adjustment often led to functional faults such as suction problems or cavitation.
Electronic technology was used for setting stroke and pause control with symmetrical suction and stroke phases. This caused poor miscibility.
Alldos Eichler has replaced the old drives with an innovative new stepping motor. The dosing rate is set precisely by adjusting the stroke speed. This advanced technology combines a highly dynamic stepping motor with a powerful microcontroller, delivering speed profiles with innovative advantages for the user.
The dosing flow is set digitally at a consistently short suction stroke and full stroke volume. The duration of the pressure stroke is adjusted to suit the specified dosing rate per hour. Since the volume drawn in remains constant, the suction of the dosing pump is optimised. This ensures balanced – almost continuous – dosing in the lower capacity range. The use of stepping motor-operated dosing pumps allows a consistently high level of dosing precision to be maintained.
Pump in action
By combining versatile stepping motor technology with powerful microelectronics, the TrueDos generation of dosing pumps opens up a whole new dimension in ease of operation and control.
The required dosing rate (l/h) is input with a single calibration exercise for the entire capacity range. Control of the contact signal with PID-controlled dosing ensures a constant dosing rate once the ml/contact data has been entered. Flexible weighting of 0(4) to 20 mA signals is achieved through analogue control. The slow mode function is particularly useful in connection with viscous media. A slower suction stroke can be set if necessary. The stroke frequency can be reduced from a maximum of 180 strokes/minute to a maximum of 120 strokes/minute for viscous media.
For batch dosing, the dosing rate can be entered per batch in either litres or millilitres. The timer function on the TrueDos D regulates the required dosing speed using input data such as batch start, batch duration and dosing quantity.
The total operating hours meter and the total dosing quantity meter of the dosing pump also make life easier when it comes to assessing cost-effectiveness. The code function protects the device against accidental adjustment or unauthorised access. This ensures that only authorised personnel can operated the TrueDos D. Non-processed contact signals are stored using the memory function, so that the pump can process them later if required. Analogue and digital interfaces and a Profibus allow additional connections to be added at any time and with minimal effort.
The capacity range of the dosing pump is 0.024 to 2.4 l/h at 10 bar and 0.2 to 20 l/h at 2.9 bar.
Three functions in one pump
In the past, constant control with setpoint-regulated dosing required three devices – a dosing pump, a flow meter and a setpoint controller. Today, only one device is required – the TrueDos M, a more advanced version of the TrueDos D.
This dosing pump for dosing rates of up to 6 l/h is capable of meeting today’s precision needs. Reliable dosing is ensured by the dosing unit with priming chamber and integrated measuring technology.
The TrueDos M is fitted with a dosing head as well as the priming chamber. The dosing pump synchronously pumps the liquid into the priming chamber at high volume and then into the dosing head by way of an integrated measuring burette. Volumetric flow measurements are taken at short intervals using a high-precision ultrasonic sensor and a solenoid valve attached to the measuring head. The setpoint entered prior to operation is constantly compared with the actual value and any necessary corrections are made immediately. The system precision here is ±1 %. The capacity range of the TrueDos M is 0.024 to 2.4 l/h at 10 bar and 0.06 to 6 l/h at 10 bar.
The priming chamber concept has other benefits for the user, which are of particular value when dosing very small quantities or using outgassing media. Suction problems when pumping and dosing tiny quantities are a thing of the past, since a high volume of liquid is pumped into the priming chamber and the excess is then fed back into the original container via a bypass. Outgassing media are degassed in the priming chamber, which prevents any dosing errors. The media container can even be changed without interrupting the dosing process, since the priming chamber always contains sufficient dosing medium to bridge it.
This dosing pump is perfect for use in applications in which constant volume and flow monitoring of the dosing process is essential. Current control via a 4…20 mA interface allows the pump to be integrated into analogue control circuits. It can also be used in regulated systems and incorporated into digital control circuits via the Profibus control. The device additionally reports any faults.
cpp 400
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