Instrumentation

The laboratory is equipped with a variety of instrumentation options, which include motion and loading sensors, as well as strain gauges. All distance and loading sensors are calibrated and documented annually.

Motion Sensors

String Potentiometers

Our string poteniometers are manufactured from SpaceAge Control and Celesco. They come in different maximum displacement options, to provide a more percise reading, depending on the project needs:

  • +/- 2 inches
  • +/- 6 inches
  • +/- 20 inches
  • +/- 25 inches

Data sheets

Linear Potentiometer

As with our string poteniometers, our linear potentiometers come in the following maximum displacement options and manufactured by ETI Systems:

  • +/- 0.25 inch
  • +/- 0.5 inch
  • +/- 1.0 inch
  • +/- 2.0 inches

Data sheet

Accelerometers

The lab is also equipped with Honeywell (formelly known as Sensotec) accelerometers. These accelerometers, model AG111, have the following performance:

  • Ranges: ±10 peak g
  • Sensitivity:
    • Nominal: 3.8 mV/g
    • Range: 2.4-5.0 mV/g
  • Usable Frequency Range: 0-400 Hz
  • Mounted Resonant Frequency: 1,000 Hz

Data sheet

Loading Sensors

Load Cells

Since many of of the test apparatuses are specifically devleoped for single experiments, in-house custom built load cells are often used. The geometric layout of a typical load cell is shown in the image below. They are fabricated from a thick wall cylindrical steel tube. The turned down wall thickness, height, and radius are determiend based on the expected maximum stress in the load cells during testing.

Geometric Layout of a Typical Load Cell.

Geometric Layout of a  Typical Load Cell

Typical Strain Gauge Positioning and Wiring for Multi-directional Load Cells.

Typical Strain Gage Positioning for Multi-directional Load Cells

The attachment plates ensure a uniform stress distribution over the entire load cell and provide anchorage into the columns. In the most complicated custom built load cells, axial, shear, and moment stresses can be measured from Wheatstone bridge circuits wired. Simpler compression-tension load cells are also commonly built using only an axial Wheatstone bridge circuit. In addition a majority of the MTS, Miller, and Parker Actuators were purchased with a load cell provided by the manufacturer. These load cells are often used in experimentation.

Load Measuring Devbice Type Quantity Load Capacity Use
5.5" Five-Component Load Cell
5D-LC-5.5-YEL
(axial, x & y shear, x & y moment)
16 Axial: 30 [133.6]
Shear: 5 [22.3]
Moment: 30 [3.39]
Shake Table
&
Floor Testing
12" Five-Component Load Cell
5D-LC-12-BLU
(axial, x & y shear, x & y moment)
1 Axial: 100 [454.5]
Shear: 20 [89]
Moment: 220 [24.86]
Shake Table
&
Floor Testing
12" Five-Component Load Cell
5D-LC-12-BLK
(axial, x & y shear, x & y moment)
4 Axial: 100 [454.5]
Shear: 20 [89]
Moment: 220 [24.86]
Shake Table
&
Floor Testing
Axial (various)
(compression:tension)
10 2 - 250
[8.9-1112.06]
Shake Table
&
Floor Testing
Washer
(compression only)
8 100 [454.5] Shake Table
& Floor Testing
MTS Load Cell 1 2.2 [9.79] MTS Actuator
MTS Load Cell 2 55 [244.65] MTS Actuator
MTS Load Cell 1 110 [489.30] MTS Actuator
MTS Load Cell 1 220 [978.61] MTS Actuator
Lebow Load Cell 2 250 [1112.06] Miller Actuator
Custom Built Load Cell 4 70 [311.38] Parker Actuator
MTS Load Cell
Model 661.31E-01
3 220 [978.61] MTS Actuator
MTS Differential Pressure Cell
Model: 660.23
5 5000 psi
[35 MPa]
MTS Actuator

For information on our 6" Five-Component Load Cell, in-house made, please refer to the below document.

Delta P Cells

Delta P cells are used on many of the actuators available in the laboratory. The MTS servo controllers utilize the Delta P (differential pressure) measured across the actuator piston as a stablilizing variable during the control of an actuator's motion.

Strain

Strain Gauge

While there are several methods of measuring strain, the most common is with a strain gauge, a device whose electrical resistance varies in proportion to the amount of strain in the device. The most widely used gauge is the bonded metallic strain gauge.

The metallic strain gauge consists of a very fine wire or, more commonly, metallic foil arranged in a grid pattern. The grid pattern maximizes the amount of metallic wire or foil subject to strain in the parallel direction (Figure 4). The cross sectional area of the grid is minimized to reduce the effect of shear strain and Poisson Strain. The grid is bonded to a thin backing, called the carrier, which is attached directly to the test specimen. Therefore, the strain experienced by the test specimen is transferred directly to the strain gauge, which responds with a linear change in electrical resistance. Strain gauges are available commercially with nominal resistance values from 30 to 3000 Ω, with 120, 350, and 1000 Ω being the most common values.

Bonded Metallic Strain Gauge.

Bonded Metallic Strain Gauge

It is very important that the strain gauge be properly mounted onto the test specimen so that the strain is accurately transferred from the test specimen, though the adhesive and strain gauge backing, to the foil itself. A fundamental parameter of the strain gauge is its sensitivity to strain, expressed quantitatively as the gauge factor (GF). Gauge factor is defined as the ratio of fractional change in electrical resistance to the fractional change in length (strain).

The Gauge Factor for metallic strain gauges is typically around 2.