MTS Landmark Tabletop - Manual (Page 34)

• The free flow configuration passes the hydraulic pressure from the HPU (or hydraulic service manifold)
through the manifold to the hydraulic components. This configuration has no pressure controls; the hydraulic
pressure is controlled by the HPU.
• The on/off configuration applies or removes high-hydraulic pressure to the load unit.
• The high/low/off configuration applies high or low hydraulic pressure to the load unit.
• The proportional valve configuration applies high or low hydraulic pressure to the load unit using a
proportional valve to ramp the pressure transitions.
Transducers
The axial load unit includes a force transducer and an LVDT to measure linear forces and displacements.
The axial-torsional load unit includes an axial-torsional force transducer, an LVDT, and an encoder.
• Force: The force transducer (also called load cell or force sensor) measures the amount of tension or
compression applied to it. It has four strain gages that form a balanced Wheatstone bridge. When forces
are applied to the bridge, it becomes unbalanced and produces an electrical signal that is proportional to
the force applied to it. The axial-torsional transducer includes two Wheatstone bridges; one to measure
linear forces and the other to measure rotational forces. Force transducers are resistive devices and
require a DC conditioner to process the signals from each Wheatstone bridge.
• LVDT: The LVDT measures the linear actuator’s travel. The LVDT consists of a transformer with one
primary and two secondary coils wound on a common cylinder. The coil is stationary inside the actuator.
A core is attached to the piston rod of the actuator. As it moves inside the coil, it produces an electrical
signal that represents the position of the piston rod. The phase of the signal indicates the direction the
actuator rod is moving. An LVDT requires an AC conditioner to process the signal.
• Encoder: The encoder measures the amount of rotation produced by the rotary actuator. It is coupled to
the rotary actuator. The absolute encoder produces a unique digital code for each distinct angle of the
shaft.
Series 661 Force Transducers
The force transducer commonly used with the axial tabletop Series 370 Load Unit is a Series 661 Force
Transducer. There is no manual for the force transducer. The following table provides the specifications for
the force transducers.
Specification Parameter
Static overload capacity 150% of rating. Capacity
15 kN Model 661.19H-03
25 kN Model 661.19H-04
20 V DC Maximum excitation input
Axial = 350Ω Bridge resistance
0.05% of full scale Hysteresis
0.05% of full-scale axial typical Nonlinearity
34 MTS Landmark™ Tabletop Load Units Product Information
Introduction