DESCRIPTION F-Control feeding controller Calibration TRE / 09.12.2009 899.470.20.02-BB-0-GB DESCRIPTION F-Control feeding controller 899.470.20.02-BB-0-GB This documentation is valid for: Software : 899.461.00.00 From XMLVersion 1.0.1.0 PFISTER GmbH, D-86165 Augsburg Page 1/6 DESCRIPTION F-Control feeding controller Calibration TRE / 09.12.2009 Contents 899.470.20.02-BB-0-GB Page GENERAL 1 The measuring system CALIBRATION 2 2 Weigh feeder load cell calibration (Prm 21.1) Weigh feeder load cell dynamic zero (Prm 21.1) .5 Weigh feeder load cell calibration check (Prm 21.1) .6 Weigh feeder load cell dynamic calibration (Prm 21.1) Weigh feeder load cell static zero point (Prm 21.1) INDEX HISTORY Copying of this document, and giving it to others and the use or communication of the contents thereof, is forbidden without express authority © PFISTER GmbH, Augsburg 2009 PFISTER GmbH, D-86165 Augsburg Page 2/6 DESCRIPTION F-Control feeding controller Calibration TRE / 09.12.2009 899.470.20.02-BB-0-GB GENERAL 1 THE MEASURING SYSTEM For the recording of weight the measuring systems are equipped with load cells These send an electric voltage to the evaluation circuit which is proportional to the force acting on the load cell During calibration the relation between a known weight (checkweight) and the display value of the evaluation circuit is fixed The force acting on the load cell and the resultant input voltage (measuring signal) at the measuring amplifier is first converted into a decimal value (digitalized) by the evaluation circuit Since this decimal value is limited by the resolution of the measuring amplifier (20 bit = 1048576), the conversion of the measuring signal can be optimised via parameters input range MF1 (46.22) and compensation of dead load MF1 (46.23) At the same time the compensation of dead load MF1 (46.23) suppresses the offset and the span is increased via parameter input range MF1 (46.22) so that only part of the input voltage measuring range is digitalized, thereby improving its resolution This results in the following relationship between the measuring signal and the decimal value: Ue [mV] + d= 1048576 x compensation of dead load MF1 (46.23)x input range MF1 (46.22) 100 input range MF1 (46.22) Ue = Input voltage at the measuring amplifier In the following diagram the conversion of the measuring signal (Ue) is displayed at various settings for the input range MF1 (46.22) and compensation of dead load MF1 (46.23) input range MF1 (46.22) = 25.15 mV; compensation of dead load MF1 (46.23) = % input range MF1 (46.22) = 12.57 mV; compensation of dead load MF1 (46.23) = -25 % (= 3.14 mV) d [d] 1000000 800000 600000 400000 2.5 Ue [mV] 200000 7.5 PFISTER GmbH, D-86165 Augsburg 10 12.5 15 17.5 20 22.5 25 Page 3/6 DESCRIPTION F-Control feeding controller Calibration TRE / 09.12.2009 899.470.20.02-BB-0-GB As can be seen, the digitalization of the measuring signal can be improved with a suitable selection of amplifier settings In this example, however, when selecting the orange-coloured characteristics curve it is important to ensure that the measuring signal remains at all times within the digitalization limits (3.14 mV | 15.71 mV), otherwise an error in the recording of the measured value will stop the feeding process CALIBRATION WEIGH FEEDER LOAD CELL CALIBRATION (PRM 21.1) References: Calibration of scale Zero curve Parameter: 41.13 41.14 46.24 46.25 The relationship between the measuring signal, decimal value and the display value are set by the actions set zero (1) and set span (2) during calibration d [d] WI1 [kg] 1000000 800000 600000 10.0 400000 0.0 200000 Ue [mV] 2.5 7.5 10 12.5 15 17.5 20 22.5 25 m [kg] 10 15 20 25 30 35 40 45 50 Due to the mechanical version of the feeding system the power transmission of the measuring section and the checkweight on the load cell are often implemented via leverage ( scale leverage (41.13) and checkweight leverage (41.14)) PFISTER GmbH, D-86165 Augsburg Page 4/6 DESCRIPTION F-Control feeding controller Calibration TRE / 09.12.2009 899.470.20.02-BB-0-GB In the above diagram a leverage of 1: is used, which means that while the dead load of the system is 40 kg, it only acts with 20 kg on the load cell The checkweight of 10 kg acts only with half its weight on the load cell, but is, however, displayed with 10 kg by the evaluation circuit through the calibration process During calibration the action set zero sets the load (dead load) as zero value due to the mechanical version of the feeding system The corresponding decimal value is saved in parameter dead load point MF1 (46.24) With action set span a factor is determined which, taking into account leverage ( checkweight leverage (41.14) ), expresses the relationship between the determined decimal value and the display The corresponding factor is saved in parameter calibration factor MF1 (46.25) calibration factor MF1 (46.25) = checkweight (31.21) [Kg] x checkweight leverage (41.14) [m] x 1000 Measured value of checkweight [Kg] — dead load point MF1 (46.24) WI1 [kg] 15 12.5 10 7.5 calibration factor MF1 (46.25) dead load point MF1 (46.24) 2.5 d [d] 38000 40000 42000 44000 46000 48000 50000 52000 54000 -2.5 -5 2 WEIGH FEEDER LOAD CELL DYNAMIC ZERO (PRM 21.1) With the dynamic zero, fluctuations of the load are compensated via a rotor or belt rotation These fluctuations are generally due to manufacturing tolerances or production methods (e.g joint in the conveyor belt in case of belt weighfeeders) The rotation is segmented (selection synchronization) dependent on the 40.13 (synchron sensor) and a separate zero value is saved for each segment During the measurement the zero value is then subtracted from the measured value for the segment currently on the measuring section If for synchronization (40.13) time based is selected, the average value is formed around a rotation (no segmentation), which is then subtracted from the current measured value during the measurement The dynamic zero thus acts as position-dependent offset on the dead load point PFISTER GmbH, D-86165 Augsburg Page 5/6 DESCRIPTION F-Control feeding controller Calibration TRE / 09.12.2009 899.470.20.02-BB-0-GB WEIGH FEEDER LOAD CELL CALIBRATION CHECK (PRM 21.1) The calibration check is purely a checking measure No adjustments or calibrations are carried out During the calibration check the setpoint and real value of the checkweight are compared and the percentage deviation is displayed WEIGH FEEDER LOAD CELL DYNAMIC CALIBRATION (PRM 21.1) For some scale types a change in environmental conditions requires a readjustment at operating temperature However, the changed environmental conditions have no effect on the zero point ( dead load point MF1 (46.24)) of the scale, but affect the span (calibration factor MF1 (46.25) ) of the measuring system This effect can be determined and corrected if necessary by the dynamic calibration during operation The dynamic calibration can be started by the operator via the FSI When sufficient material has been conveyed by the feeding system the operator must stop the dynamic calibration The value determined via an external comparator system (scale or silo) can then be entered in the FSI With the takeover of the calculated correction value the span is then corrected This correction value can also be entered directly in the FSI (correction calibration MF1 (46.26)) and is retained also after a new calculation WEIGH FEEDER LOAD CELL STATIC ZERO POINT (PRM 21.1) The sequence contains only a partial calibration at which only the dead load point MF1 (46.24) is newly determined When setting the static zero point also the reference of the dynamic zero is lost, so that subsequently it is necessary to carry out the dynamic zero sequence INDEX HISTORY Index Author Date of issue Modifications Herz 09.12.2009 First issue Subject to change without notice The technical data and specifications are valid at the time of publication of this documentation The information provided in this publication is, however, checked on a regular basis and any necessary corrections made in subsequent editions Pfister GmbH reserves the right to alter these versions at any time We are always grateful for suggestions for improvement PFISTER GmbH, D-86165 Augsburg Page 6/6