Structured Variable Description

OVLD (i_stOVLD)

A structure of the data type OVLD containing configuration parameters.

wSpdDbnd

To be able to measure the actual torque correctly, constant speed is needed. Therefore the FB is only starting to engage into the torque sampling, once the measurement frequency is reached. Depending on the settings of the speed loop of the drive the actual speed is oscillating around the target speed. To compensate this irregularity a dead band around the target speed is needed.

The FB defines target speed attainment as:

actual speed > ( target speed – wSpdDbnd )

and

actual speed < ( target speed + wSpdDbnd )

wTrqBndCnt

During starting and acceleration the torque of the drive is oscillating. To measure the actual torque correctly, the FB is waiting until the torque has settled and becomes relatively constant. This parameter is the number of cycles the torque values from the drive need to be inside the torque dead band defined by wTrqBndWdth to start the measurement.

wTrqBndWdth

Depending on the settings of the speed loop of the drive, the actual speed is oscillating around the target speed. To compensate this irregularity a dead band for the torque is needed. The FB starts counting values to fulfill wTrqBndCnt if the actual torque values are:

actual torque > ( actual torque of the last cycle * ( 1.0 – wTrqBndWdth ))

and

actual torque < ( actual torque of the last cycle * ( 1.0 + wTrqBndWdth ))

wSmple

This is the number of samples (equaling controller cycles) that are taken during the torque measurement. The resulting value is the average of all samples.

dwLoadNom

This is the nominal load of the hoist. If the nominal load is variable (e.g. changing based on the position of the trolley on a jib of a tower crane) this value must be updated continuously to reflect the actual nominal load.

wMeasFreq

This is the frequency in RPM at which the torque measurement is conducted. It must be bigger or equal to the LSP setting of the drive. The smaller the value chosen, the earlier the measurement will result in overload detection. We recommend setting this frequency higher than the slip of the motor, even when running in closed loop.

wTrqThres

This is a percentage of torque to detect a change in load after the torque measurement. If the actual value of the torque rises beyond this value, the drive is decelerated to measurement frequency again and the torque is measured one more time. Make sure to set the value above the normal rise of the torque during acceleration with a constant 100% load.

wAntiTip

From the start of the upwards movement of the hoist the distance is monitored. After a successful measurement of the torque the monitoring is disabled. The FB will compare the actual distance with the desired number of turns entered into this parameter. This is necessary to help prevent the user from inching the load upwards without performing a load measurement, and thereby allowing an excessive load to be lifted without triggering an alarm. If wAntiTip is engaged, it will stop the upwards movement by setting the overload alarm output to TRUE.

If i_stOVLD.wAntiTip is at 55 turns and i_stOVLD.wEncPuls is at 1024, the maximum distance available to measure the load is 55 x 1024 = 56320.

It is helpful to look at the q_wStat output of the FB during commissioning.

wNoTrq

This is a threshold of torque in percent.

Below this threshold value the measurement procedure is disabled.

If the motor is running with very little load, the actual torque value of the drive has high oscillations. Therefore any torque measurement in this range would be too inconsistent to use in application.

rOvldThres

This is the tolerance adjustment of the overload detection. It can be set between 0% to 20% tolerance.

If the maximum torque at 100% load is set to 10000, and rOvldThres is set to 1.1, a measured torque of 11000 must be exceeded to detect overload.

xEnLdCell

To enable the usage of a load cell instead of using the torque of the drive, this bit must be set TRUE. The signal of the sensor must be scaled to 1 kg. The measurement run at lifting up will be disabled. All signaling, the overload alarm, the 90% alert, the lamps and the horn remain active.

The input pin i_rDrvTrqMax does not need to be connected.

rAcuWght

This is an optional dividing factor to the q_ wActWght output. By default it is set to 1.0 which puts the weight output to a scaling of 1 kg.

This value is helpful for a display. A value of 123 with a scaling of 10 can be used to show the actual weight in tons with 2 decimal places.

wActWghtThres

If the hoist is used with no load or little load, the torque value of the drive is not always reproducible and steady. Therefore it is possible to disable the actual weight output below a certain load, it will then always be zero. If you put a value of 1000.0 to this input, all loads below 1000 kg are represented as 0 kg. Depending on the mechanical circumstances of the crane the threshold for reproducible and steady results is at around 30% of the available torque of the drive.

dwCalbWght

This is the weight value in kilogram used during the calibration, that means, the calibration bit i_stOVLD.xCalb is TRUE. All internal calculations of the 100% load threshold are based on this value, therefore it is very important to measure the weight used precisely. If calibration is inactive this input does not have any effect.

xCalb

This is the switch to enable calibration. If the input i_rDrvTrqMax is left at zero the result of the calibration is used to analyze the load. If any value unequal to zero is entered at the i_rDrvTrqMax input, it will override the calibrated result.

Refer to the calibration procedure description.

xOvld

This is the switch to enable the overload test during the acceptance test for a new crane.

If set to TRUE, it enables to lift loads with up to 300% torque. It can only be active for a maximum of 5 hours of movement. If left active for longer than 5 hours an overload alarm will be triggered preventing the upwards movement of the hoisting axis.