Dr. Livingstone, I Presume WELDWISE 2400 - Manual (Page 96)

0434-INS-400 Rev. C
7-2
Types of Sensors
Current:
A Livingston-supplied toroid must be used with a Livingston weld monitor. No substitutions can be
made.
Voltage:
Livingston uses voltage leads to read incoming voltage signals and to calibrate the weld monitor.
These leads are typically included with the Livingston shipment.
Force:
A variety of force sensors is available for use with Livingston weld monitors:
• Load Cells: Possibly the best for measuring small changes in force, a load cell measures directly
from the electrode tooling and is therefore not susceptible to changes in force readings related to
seal leakage, sticky cylinders or valves, etc. Load cells are generally designed into the tooling of
the weld head by the machine manufacturer. Due to the time and cost of tooling modification, this
type of sensor may be less desirable when installing in a retrofit application.
• Weld-Thru Load Cell: This sensor works very similar to the above load cell, but installs directly
into the weld loop so that weld current can flow right through the sensor. This particular load cell
comes with a male and female RWMA taper and is perhaps the easiest to retrofit, although there
are a few issues to consider: Approximately 1.75” of adjustment at the electrodes is required for
sufficient clearance of the sensor body and cable to incorporate it into the weld loop.
• Pressure Sensors: These sensors are typically small transducers that connect to the supply line of a
hydraulic or pneumatic cylinder. They work by sensing the pressure driving the piston attached to
the rod that applies force to the work piece. Typically, these sensors show less detail and are less
sensitive than a mechanically connected load cell, but still provide valuable data about the
consistency of weld force.
Hydraulic: Excellent results can be achieved by installing a hydraulic sensor into the hydraulic
cavity of an air over oil type cylinder (not into the intensifier line). The intensification
of a small amount of oil gives a very high resolution that can show minute changes in
force. This arrangement provides force measurement nearly as good as a load cell,
however it is susceptible to problems caused by leaky seals, cylinders, or air in the
hydraulics.
Pneumatic: Typically installed in the airline feeding an air cylinder, the problem with this type of
sensor is that it measures line pressure rather than tip force.
The type of sensor that is best depends entirely on the application. The best performing solution is a
pancake load cell built into the weld tooling, while the next best solution— a hydraulic pressure
sensor— requires having an air over oil cylinder. A pneumatic sensor can be used with an air cylinder,
but the force reading will be less accurate due to the compressibility of air. Ultimately, any of these
sensors will work well; the choice is up to the user.