Pickering's 3U PXI Module Chosen for Diesel Engine Temperature Simulation
A world market leader for large diesel engines, whose products are used in ships and power stations. Some of these diesel engines are being manufactured for a new class of container ships, which are among the world’s largest cargo carriers.
The controllers for the massive diesel engines in ocean going vessels require many temperature sensors in order to determine whether the engine is operating correctly. The reason for so many is primarily because of the sheer size of the engine block. Meaning that many sensors are required to ensure that the engine operates in the correct temperature range and that hot spots are identified quickly. It would be difficult to have an engine block available for system test, not to mention the time it would take for the engine to reach operating temperature. Sensor simulation provides a cost-effective means of testing the controller, without having an engine on hand.
This requirement involved the support of ECU (Engine Control Unit) development for 40,000 kW ship diesel engines. In terms of horsepower, 40,000 kW equates to approximately 55,000 HP. Besides other ECU tasks, there was a requirement to simultaneously simulate 144 channels of PT100 temperature sensors. These sensors are RTDs (Resistive Temperature Devices) as opposed to thermocouples. The temperature range in this requirement was -20ºC to +250ºC, with an equivalent resistance range of 92.160342 Ω to 194.074250 Ω. Extreme precision was also required, demanding accuracies within 0.11ºC at -20ºC (equivalent resistance deviation within 43mΩ) and 0.65ºC at 250ºC (equivalent resistance deviation within 220mΩ).
The customer’s original method of sensor simulation was achieved manually. The method comprised 288 precision potentiometers (covering both coarse and fine adjustment), along with 144 switches for short circuits and anther 144 switches for open circuits in the simulation of faulty wiring connections to a sensor. All of these components were adjusted and controlled by hand. The need for automation was obvious in order to save time and improve performance and repeatability.
The solution developed was a 3U PXI module (model 40-262) that supports either six channels of RTD simulation (in one slot) or 18 channels (in two slots). Based upon existing design principles, the module provides a setting resolution of 2mΩ and a resistance accuracy of better than 0.1% on all channels. Each simulation channel can provide a short or open circuit setting, in order to simulate faulty wiring connections to a sensor. Furthermore, the calibration or verification of each resistor channel is possible by connecting the module calibration port to a high-performance DMM (Digital MultiMeter). The use of simple resistance value calls makes programming simple, using an API (Application Programming Interface) to convert temperature request to resistance request through a model of the sensor used in the real engine.
The end product enabled a cost effective method of simulating either PT100 or PT1000 RTDs, with very high accuracy. Eight modules achieved the 144 channels of PT100 required in this application (18 channel two slot modules), accommodated in sixteen slots of 3U PXI chassis space.