Screw compressors with motors over 22kW are, as a standard, equipped with the AIRPOL-POWER-CONTROL microprocessor controller. Its task is to supervise and to control operation of all sort of screw compressors, considering different options that result from various power of the machines and specific work environment. At the design stage the latest development trends in the area of compressed air technique have been taken into account.

Our goal was to create optimum compressed air control system, bringing economical effects by increasing energy efficiency together with safe electric motor operation.

Energy saving is achieved by constant measurement of motor temperature and idle running time adjustment. When the motor is not warmed up enough the controller shortens time of idle run, switching the compressor earlier. Idle run time is enough only for discharging and a safe stop. However, when motor temperature exceeds the factory set value, the controller prolongs the idle run time until the motor temperature is cooled down. The advantage of that control system is an immediate availability of the compressor for the next run. A parallel measurement of temperature and current gives the best failure protection of the motor - better than standard thermo-bimetallic transmitter.

The AIRPOL-POWER-CONTROL controller is responsible for controlling and adjusting work of the compressor in an economical way. The operator is informed about all significant work conditions and all set values of the compressor.

When creating the microprocessor controller, we focused on easy operation and clear way of changing parameters and displaying them. In order to achieve that we created legible text display symbols arranged in a logical way. There is also a possibility of changing displayed language (Polish, English and Russian) when required.

On the controller's front, beside the display there are LED diodes that indicate the most important compressor's conditions.

There are only four buttons (beside START and STOP) to change compressor's work parameters. Operation is thus simplified with no need to permanently consult the manual. Some of the important compressor's work parameters can be protected with password, which precludes the unauthorised personnel from changing them.

The following parameters are displayed on the control desk: minimum pressure, maximum pressure, current work pressure, current oil temperature, current motor temperature, idle run time, chosen work mode.

The controller in question is accompanied by the MsConnect.exe application for Windows. The software enables communication between the controller and the computer through a RS-232 serial connector. The task of that communication is to visualize (to monitor) entire work of the compressor or a group of compressors.
The programme performs the following actions:

1. Recording current parameters of the compressor work:
- current working pressure,
- upper and lower limits of working pressure,
- motor temperature,
- oil temperature,
- number of hours of work,
- value of electrical current drawn by the compressor,
- time of work in idle running.

2. Modification of settings of the above-mentioned parameters.

Recording current parameters of the compressor work

3. Recording of graphs:
- value of pressure in the function of time and,
- value of electrical current drawn by the compressor in the function of time.

4. Report of the compressor work along with the specification and interpretation of the last 16 errors in operation.

As a standard, all AIRPOL-POWER-CONTROL controllers are equipped with a real-time clock, which makes it possible to switch the compressor on and off at a pre-defined time (on a given day, at a given hour and minute).

Recording of graphs

Optionally, the controller may be equipped with steering and monitoring function enabled by means of the GSM network. After the installation of a special GSM modem (or using a GSM telephone equipped with an RS-232 interface) in the AIRPOL-POWER-CONTROL controller, the operator has the option to remotely communicate using his mobile phone. All information about the parameters of the compressor work (compressor status) as well as any messages signalling failures are sent from the controller in the form of short text messages (SMS). Also, the operator can modify compressor parameters using his mobile phone.

The connection of the controller with an Ethernet module enables the remote control (in real time) of the compressor(s) via the Internet. This is particularly convenient while operating compressors in remote places with no regular supervision. For the sake of convenience of servicing, it is also possible to use a transponder card connected to the controller connector, which records all status parameters of the compressor and a list of errors. The card can be sent to the producer and its contents can be read on a PC computer.

Control system of a group of compressors makes it not necessary for the staff to adjust the settings, saves electric energy and assures equal work load.

Supervision and control over a group of compressors connected to a compressed air network is possible with use of controllers: AIRPOL-POWER-CONTROL-type (as a standard in over 22kW compressors) and 230RC (fully independent external controller). The 230RC controller is intended for compressors equipped with traditional control devices and reciprocating compressors. Pressure converter is supplied with the controller, and the pressure value is set on the controller to considerably simplify system's operation.

As a standard, each controller is supplied with software specially designed for controlling a group of compressors. It is possible to choose between sequential control and cascade control. The maximum number of compressors that can be connected to form a compressor unit is 8. The compressors communicate with one another by means of the RS 232 serial connector. Sequential control is recommended for compressors of comparable size. The user specifies only the upper and lower values of the pressure to be maintained in the air tank and the time of parameter rotation. Other settings are executed by the controller (including the division of pressures of connecting individual compressors). The controller of the compressor marked with number 1 takes on the function of the main controller, and it constantly controls the state of other compressors. If any of the compressors breaks down, the controller excludes it from the system, and the compressor unit continues its operation using the remaining compressors. The whole system is switched on and off, and main parameters are monitored by the main controller, which considerably facilitates the controlling process. The computer which forms a part of the system enables the remote control of the whole system and facilitates its servicing, as there is the possibility of reconstructing the whole history of work of the compressor within the operation period.

When requirement for compressed air varies significantly in time there is a possibility of connecting several compressors of comparable size with the frequency converter. Then one machine is controlled by the converter, and the others operate in a traditional way: START-LOAD-IDLE RUN-STOP. Efficiency adjustment with use of the frequency converter has another advantage which is, apart from smooth adjustment to current air consumption, maintaining the same level pressure value in the network. Pressure in compressed air network is measured by means of a pressure converter with electric current output which is connected to the PID regulator of the frequency converter. There is also an extension card available in the frequency converter containing software that enables controlling a group of compressors without additional master controller.

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