The AMX 211 module is a device designed to control the combustion engine - dynamometer set-up. It actually uses two PID software controllers working independently of each other to automatically adjust the controlled variable to hold it at the set-point. The AMX211 controller can operate in five different modes:

• Mode 1 - steadies the set RPM of the engine using the dynamometer exciting current; setting the actuator servomechanism at the assigned position;
• Mode 2 - steadies the set load torque of the engine using the brake exciting current; setting the actuator servomechanism at the assigned position;
• Mode 3 - steadies the set RPM of the engine using the brake exciting current; steadies the torque by adjusting the position of the actuator servomechanism;
• Mode 4 - steadies the set torque of the engine using the brake exciting current; steadies the set RPM of the engine by adjusting the position of the actuator servomechanism;
• Mode 5 - steadies the set torque of the engine using the brake exciting current in compliance with its square characteristics, setting the actuator servomechanism at the assigned angle;

The operator switches between these modes selecting the appropriate function keys: . These function keys are located on the module's front panel.

The controller can use the following sources of set-point values:

• setting potentiometers located in the AMX 211 front panel;
• a PC computer using the RS232 or RS485 interfaces;
• external input voltage (0 - 10V).

The input source can be selected using the key. The AMX 211 unit is used to program and supervise test trials. The testing program consists of sets of operation points (cycles) repeated cyclically until the test time is complete. Each cycle consists of a certain number of steps. A single step can be defined just as a certain operating point of the engine held during a certain period or until one of the controlled temperature/pressure values reaches the set threshold. Each step or cycle can be automatically repeated any number of times. The test time is recorded, and each time the test program is interrupted an appropriate log entry is written to the non-volatile memory so that the program can be resumed at some later time (for example, the next day) if necessary. At each operation point measurements are taken of all the necessary parameters of the engine operation (fuel consumption, pressure, temperature, torque, RPM). Measurements are also taken at the start and completion of the test program. All recorded data are stored in the RAM memory (of the 16 kB capacity) sustained by batteries, or in the FLASH memory (of the 1MB capacity). Then the test results can be printed through the RS232 interface on a serial printer, or be accessed directly using a computer with the appropriate software. Operation cycles can be programmed in the following two modes:

1. The mode that does not verify the set point of operation. This mode makes it possible to program any operation points, whether accessible or not (for the given engine power, RPM, max. torque);
2. The mode that does verify the set point of operation. Entered values must be values set for the working PID controllers, so entered operating points are verified.