R&M Materials Handling HOIST MONITORS - Manual (Page 22)

R&M Materials Handling, Inc.
4501 Gateway Boulevard
Springfield, Ohio 45502
P.: (937) 328-5100
FAX: (937) 325-5319
22/105
R&M Materials Handling, Inc. reserves the right to alter or amend the above information without notice.
Fault means that one (or more) of the supervised safety features values exceeds the limit. Running the
hoist is restricted.
For Run or Fault supervision, it is possible to connect an external indication device like a horn or
lamp to the relay output. Relay output must be programmed to the desired function “OK” or “Ready”
5.2 Overload protection
The overload protection can be done in two ways, either with motor torque calculation or by using a load
sensor. Regardless which system is used, the hoist-monitoring unit will prevent the hoisting motion when
the measured load exceeds 110% of the rated load for a period of time. A filtering delay is built in to
assure trouble-free lifting of a rated load. The overload protection is reset when the measured load
decreases to 80% of the rated load.
The overload protection reacts faster than the display updates the measured values. Therefore it
may happen that the movement is stopped although the display indicates a load less than 110% of
the rated load.
Overload level Filtering time Run-down time
140% 60 ms ~100 ms
125% 200 ms ~250 ms
110% 1000 ms ~1050 ms
The motor torque calculation system uses the motor voltage, current and temperature to calculate the
motor torque and converts this into load information. This system cannot be used in combination with
frequency converters, and can only measure the load when the motor is running. In addition to the
overload protection, the hoist-monitoring unit also supervises the brake. When the calculated load value
descends under -50% of the rated load during lowering, it indicates that the brake did not open. Lowering
the hook is prevented, but lifting is still allowed.
Motors driven by a frequency converter are always equipped with a load sensor for load measurement.
Systems using a strain gauge type of sensor are also equipped with a load sensor amplifier to amplify the
signal coming from the sensor. In case a Hall-type of sensor is used, the load sensor amplifier is not
needed.
Param. Name Value Description
4-7 Load param Load calculation parameters
Selects the load calculation method:
NU Not used, the display show all time to 0,0t
Motor Motor torque calculation. Refer to chapter “Overload protection – Motor torque” of this manual
4-7-1 Load meas.
Sens. Load sensor measurement . Refer to chapter “Overload protection – Load sensor” of this manual
Load measurement tolerance is ±10% of nominal load by use motor torque calculation system and
load measurement tolerance is ±5% of nominal load by use load sensor.