Pipe Length Measurement.
This measurement system is designed to measure the lengths of steel pipes as they
pass along a roller conveyor. The pipes range in length from 6 meters to 15 meters.
The length is measured by means of a wheel of circumference 600mm, which is
fitted with a shaft encoder producing 600 pulses /rev and is brought into contact
with the pipe pneumatically.
As the conveyor is only 18m long, a set of
three 'laser beam' detectors are used to start
& stop the counting of the pulses from the
encoder. One detector triggers count start
and the other two are used to determine the
count stop; one is used for pipes of 6m
length and the other for the longer pipes.
The distances between the three detectors
are stored within the measuring system and
are used to add the appropriate offset to the
counts from the measuring wheel. The
measuring system also requires a reset signal
from the production PLC to indicate that a
pipe is entering the system.
The measuring system comprises a dedicated real-time control computer which is
housed in a metal enclosure. On the front of which are various operator controls
and an LCD screen, on which the pipe lengths are displayed. The lengths are also
transmitted via a serial link to a large electronic display, and via a separate serial
link to a Pipe Marking Machine. In addition pipe lengths can also be sent, together
with date/time, to a small panel-mounted printer located in a control cabinet
adjacent to the measuring system.
The system enables various configuration parameters to be entered using a simple
menu structure. This data is stored in battery-backed memory and is not lost if the
system is powered down.
The control computer used in the length measuring system is programmed in a
high-level multi-tasking control language, which is an object-orientated real-time
control language similar to PASCAL. The system was shipped out to Saudi Arabia in
2001, for the customer to self install. A visit was made in 2008 to install software
updates requested by the customer.
The accuracy was such that repeated measurements on the same pipe, which
precessed axially by a small amount at each pass, showed a sinusoidal variation in
length which was found to correspond to a slight angle of the cut end of the pipe!
