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Terminology for level sensorsSwitching Point Capacitative level sensors react to conductive materials and non-conductive materials with a dielectrically constant Epsilon >1. The switching point depends on the material. When the sensor-tip is immersed in a fluid, a switching command inside the device is triggered. This trigger is set between contact with the liquid and some mm more into the liquid. This distance between the tip of the sensor and the trigger is the nominal switching point. The immersion-distance has a negative sign, e. g. -8 mm. The following table lists the approximate values for the material dependent reduction factors. In practical applications there could be variations, because of the mounting conditions, for example.
The water content of an object or a liquid has a decisive influence on the switching point. A high humidity content increases the switching point considerably.
Switching point sp The switching point or rated operating distance is a device parameter that does not take into account sample variances and external influences such as temperature and supply voltages. Optical sensors switch by immersing the tip. When the sensor tip is immersed in a fluid, the switching point has a negative sign. Effective operating distance sr The effective operating distance is the operating switching point at nominal voltage and at nominal temperature of 23°C. It is between 90 % and 110 % of the rated operating distance. Usable operating distance su The usable operating point is in the entire allowable temperature and voltage range is between 80 % and 120 % of the effective operating distance. Assured operating distance sa The assured operating point takes into account all the external influences, sample and media variances and is in the range from 0 % to 72 % of the rated operating distance point. Within this range a guaranteed switching is ensured. Switching point drift The operating distances are given for an ambient temperature of 23°C. In the permissible temperature range the switching point varies by less than 15 % from the value at 23°C. The temperature of the measured object has no influence on the switch point. Hysteresis H The switching hysteresis describes the distance between the turn on point while immersing in the liquid and the turn off point during the separation of it from the sensor. The hysteresis brings about a stable switching signal even when there are vibrations, temperature drift, or electrical failures. The hysteresis is defined according to EN60947-5-2 to be a maximum 20 % from the real switching point, and carries a value of typically 10 % from the real switching distance sr for our sensors. Repeating accuracy R The repeating accuracy describes the maintenance of the switching point after the repeated immersing in the liquid under specified circumstances. Our sensors have typical tolerances of less than 3 % of the effective operating point. Switching frequency The maximum switching frequency of the sensor is determined at nominal switching point Sp when immersing in the water. Supply voltage The operating voltage is the voltage range in which EGE sensors function safely. For a constant voltage supply it is important to make sure that the limits are still observed when the residual ripple is included. Switching current The switching current indicates the maximum continuous current for the switching output of the sensor at a given ambient temperature. The current carrying capacity is reduced with increasing ambient temperature and is meant for the use of a non inductive load. Short circuit protection The short circuit proof ensures the sensor against destruction through a short circuit on the output. After removal of the fault, the output is reactivated. Where a maximum overload current is listed, this should not be exceeded. Overcurrent release This value indicates the median value of current at which the short circuit protection responds with a tolerance of ± 20 %. Reverse polarity protection The reverse polarity protection prevents destruction of the sensor by a reversal of the polarity of the voltage supply. Voltage drop Ud The voltage drop arises in the semiconductor elements of the sensor. It is measured on the active output. Residual current Ir The residual current flows in the load current circuit when the output is blocked. The residual current must be considered when switching sensors in parallel. Minimum load current Im The minimum load current is necessary for flawless operation with two-wire devices. Current consumption The current consumption is the maximum value of the no-load current Io that the sensor can absorb without a load. Ambient temperature The ambient temperature indicates the maximum allowable temperature range for the sensor. Electromagnetic compatibility EMC The EMC class is a measure of the noise immunity of the sensor against external electrical and magnetic influences. The information is based on the standard EN 61000-6-2. Switch-on impulse suppression these sensors have a switch-on impulse suppression that blocks the output during the switch-on phase, when the operational voltage is applied. Protection The protective system indicates the protection of the sensors against penetration of foreign bodies and water according to EN 60529. LED-Display These sensors have yellow light-emitting diodes which indicate the switching status optically. Housing material The housing material determines the chemical resistance of the sensor against external influences. For special applications, other housing materials are available. Connection The connection of the sensors is accomplished through plug-in connections or cables. Different cable types and lengths are available upon request.
All pages in section: Level Sensors
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