Accessories such as temperature and humidity sensors, pressure transducers, signal amplifiers and pulse counters for energy measurement round off the E*LDS system for the control and automation of commercial and industrial refrigeration systems.
E*LDS system accessories
Temperature measurement and line resistance
Temperature sensors are probably the most frequent refrigeration system accessory. What matters here is the right choice, because line resistance in long distance cables may cause considerable temperature measurement errors, particularly where case controllers are centrally installed in the switch cabinet.
Even in two-core cable distances of around 5 m (cross-section 0.75 mm²), temperature measurement with PTC temperature sensors such as the Pt1000 may entail errors of almost 1 Kelvin.
CAN bus repeater and long-distance service
Is there any better way to explain the designation “E*LDS – Eckelmann Long Distance Service” than by expounding the function of the repeater? It is used for connecting E*LDS components over long distances, the physical features of the CAN bus segment being limited to a distance of 500 m. An additional benefit of the repeater is that, in the connection of two buildings, it galvanically separates the different potentials.
Another indispensable accessory is the modem for dial-up access to the E*LDS systems. Next to the standard modem, a hybrid modem with analogue interface and ISDN connection is available.
Background: measuring, controlling, connecting
A control loop is a closed sequential procedure that exerts its influence on a physical quantity in a process. What is crucial in this process is, to put it simply, the feedback of the actual value to the controller (negative feedback) and the continuous comparison of target and actual value.
To function properly, control systems essentially rely on actuators (for the conversion of the controller signal), and sensors. Sensors and actuators function as interfaces with the process reality.
In a refrigeration system, the correct and precise measurement of temperature and pressure has a substantial impact on the control quality, because the intelligent algorithms of case and pack controllers, for the computing procedure, have to make do with the information supplied to them by the sensors.
Modern refrigeration systems consist of numerous interacting control loops which need to be networked with one another. All field devices – i.e. sensors and actuators – are safely connected with the controller. This artificial “nervous system” is necessary for the optimal control of refrigeration systems.