In this chapter

Chapter 7 of 13

  1. 7.1Setup
  2. 7.2Two paths, two converter stages
  3. 7.3Power supply
  4. 7.4Open item before mains operation
All chapters
  1. 01Initial situation
  2. 02Objective and approach
  3. 03State of the art
  4. 04Requirements
  5. 05Solution approaches and concept decision
  6. 06System architecture
  7. 07The test rig
  8. 08The heated-tank model
  9. 09The simulation cycle
  10. 10Five test scenarios
  11. 11Result and limits
  12. 12Outlook
  13. 13Preliminary projects

Chapter 07 System

The test rig

Mounting wall with power supply, converter level and control panel

By Chapter 7 of 13 3 min read Updated: 30 September 2026

Summary

The test rig is built as a wired mounting wall. The controller is connected to the signal bridge via two galvanically isolating converter stages: optically on the forward path (24 V to 5 V), via potential-free relay contacts on the return path (5 V to 24 V). Two power supplies with separate reference potentials supply the two levels. Before mains operation, a component replacement and the initial inspection by a qualified electrician are still outstanding.

Setup

The test rig is not a laboratory setup on a table but a wired mounting wall. On the front are the controller (Siemens LOGO!), the control panel with twelve push buttons, the indicator lights, the housings of the converter assemblies and the screen of the running simulation. Power supplies and the wiring of the signal level are on the back. How the setup is embedded in the overall architecture is shown in Chapter 6.

Controller, control panel with 12 push buttons and indicator lights, and the screen with a running simulation (the picture shows the compressed-air plant).
Test rig, front: controller, control panel and screen of the running simulationSource: Own photograph

Two paths, two converter stages

The controller works at 24 V, the signal bridge (an Arduino Mega) at 5 V. Each direction therefore has its own converter stage:

  • Forward path (controller to simulation): The outputs of the controller switch the emitting diodes of an optocoupler assembly (PC817); the phototransistor in turn delivers 5 V to the signal bridge. The transmission is optical; there is no conductive connection between the 24 V level and the signal logic (Fig. 14a).
  • Return path (simulation to controller): Via a driver stage, the Arduino switches a relay assembly. Its potential-free contact applies 24 V to the input of the controller, in parallel with the push button on the control panel, so that push button and relay contact have the same effect (Fig. 14b).

The channel counts of the two paths are given in the key figures of the platform.

24 V to 5 V via a PC817 optocoupler: optical transmission without a conductive connection.
Fig. 14a Signal path forward: 24 V to 5 V via optocoupler, galvanically isolatedSource: Own illustration
5 V to 24 V via a potential-free relay contact, in parallel with the push button on the control panel.
Fig. 14b Signal path return: 5 V to 24 V via a potential-free relay contactSource: Own illustration

Power supply

One power supply generates the 24 V for the controller, control panel and indicator level from 230 V. A second one supplies 5 V for the signal bridge and 12 V for the relay coils. The reference potentials of the two levels are deliberately kept separate (Fig. 4). Every signal must therefore get from one level to the other without a conductive connection; this is the actual reason for the two converter stages.

Power supplies, reference potentials and wiring of the signal level: 230 V → 24 V for the controller, 5 V and 12 V for signal bridge and relay coils.
Fig. 4 Cabling of the signal level with both power suppliesSource: Own illustration

The electrical design is documented by the circuit diagram (Fig. 13). It is drawn in detached representation and contains the self-holding of the contactor -Q1 and the emergency stop.

Detached representation of the test rig with self-holding and emergency stop; symbols according to DIN EN 60617, designation according to DIN EN IEC 81346-2, terminals according to DIN EN 50005.
Fig. 13 Circuit diagram 230 V in detached representation, with self-holding and emergency stopSource: Own illustration
Wiring of the signal level: power supplies, optocoupler assembly, relay board and signal bridge.
Test rig, back: power supplies, optocoupler assembly, relay board and signal bridgeSource: Own photograph

Open item before mains operation

Not yet completed

The miniature circuit breaker -F2 is to be replaced with a two-pole one; after that, the initial inspection by a qualified electrician is due. Both steps are prerequisites for operation in everyday training (Chapter 12).

How the signals are processed in the model after conversion is described in Chapter 8; the timing sequence follows in Chapter 9.