Automotive and Medical Applications of High Temperature Strain Gages in Hostile Environments

Strain gages are important components in engineering research and development for the direct measurement of the stress that occurs over the lifetime of a system.

HITEC has more than 85 years of experience in precision strain measurement, having worked with a wide range of different customer supplied systems. HITEC can assist with strain measurement on-site or off-site and for strain measurements in harsh or high temperature environments.

Automotive Applications

Strain Gage Measurements on Rotating Shafts

Components can be transducerized without needing an additional torque sensor by fixing a strain gage onto a rotating shaft. This facilitates direct rotational measurements that are sensitive to the load on the torque.

Calibration of these measurements is achieved by static loading of the shaft and predictive calculations. HITEC’s partner, Developments, Inc., can also provide a wide range of custom torque sensors for any other torque measurement requirements.

Window Force Measurement

Power driven doors, windows, lift gates and sunroofs can potentially trap or pinch the user’s limbs as they open or close. To stop this from happening HITEC has produced obstruction detection sensors to determine the force applied and prevent injuries through trapping.

These sensors mount on the glass of the window and oversee the closing of the window. The sensor can be designed with custom distances and spring rates, allowing one sensor to be used in several applications.

Strain Gage Measurements in Diesel Engine Bolts

To measure bending and axial loads in a diesel engine or heavy duty truck components, encapsulated general purpose strain gages were applied in half bridge patterns, 120 degrees apart on the bolt shank, at elevated temperatures up to 550 oC.

Bolts can be instrumented with strain gages to verify torque specifications by measure clamping force.

Custom Seat Belt Force Measurement

HITEC has transducerized (i.e. custom designed) the mechanism used in seat belts to determine the extent of tensile force applied by replacing the seat belt force transducer with strain gages.

Load Sensors on Trailer Axle Hubs

The process that determines the level of preload for axle bearing can be evaluated using semiconductor-based strain gages in a full bridge configuration.

Spare Tire Lift Force Sensor

Many modern SUVs hold a spare tire securely in place under the automobile using a cable. If this cable becomes slack it can experience a significant cyclical force as a result of the tires inertia, and this force can weaken the cable or, in the event of a crash, the cable can snap resulting in the tire being flung out.

HITEC has developed a sensor which sits between the spare tire rim and the cable, where it can monitor cable tension during use to ensure that it is of adequate tightness.

Exhaust System Strain Gage for Durability Testing, Destructive Testing and Stress Evaluation

HITEC are experts at setting up strain gages for use in normal conditions or for use in high temperature applications such as in automotive exhausts. Strain gages can be welded onto high temperature surfaces using ceramic cement or with Rokide™ Flame Spray for destructive testing, temperature stability testing and stress evaluations.

EGR Cooler Instrumentation for Validating Surface Temperature Distribution and Stress Detection

In diesel-powered engines exhaust gas recirculating coolers are used to exchange heat, where cooler air is sent back to the engine to reduce the volume of NOx produced.

Strain gages can be used to determine the distribution of temperature and to monitor for any stress that could result in failure. The measured strains can be compared with temperature measurements (from an IR camera) and the results of CFD simulations.

Medical Applications

Prosthetic Knee Transducer

HITEC worked with an innovative bioengineering company that produced prosthetic limbs to determine the force applied on their artificial joints.

HITEC incorporated their semiconductor strain gages into the artificial limb and also designed temperature compensation methods for accurate measurement.

Upstream Occlusion Sensors in Peristaltic Infusion Pumps

HITEC has helped to produce strain gage transducers for the measurement of pressure changes in peristaltic infusion pumps.

When an infusion passes through the tubing an outwards force is applied which is recognized by the sensor. It the tubing becomes blocked this is registered by the sensor and an alarm is registered.

Strain Gage Transducers for Surgical Table Weight Feedback

The correct positioning of a patient influences surgical outcomes. Weight and position feedback is possible during surgery using transducer-based single-grid linear-pattern strain gages.

HITEC analyzed an existing table design and retrofitted their own system to a table to improve this functionality.

Force Measurement in Laparoscopic Surgical Instruments

The forces applied to minimally invasive surgical tools can be measured using strain gages.

For example, when strain gages are installed on trocars (used in complex laparoscopic surgery in the abdomen) they can measure force in the X and Y directions, enabling more insight into the working site, as well as internal and external pressure measurement.

Directional measurements are made possible using full bending bridges and sterilization is ensured with protective coatings and adhesives.

High-Temperature Strain Gages (Hostile Environment)

Strain gages designed for use in high temperature applications are weldable and come attached to a stainless-steel platform which is already wired and protected by a temperature resistant coating. When needed, weldable strain gages can be pre-formed.

The shim material used tends to be 0.005” Nichrome or 0.005” Inconel. Lead wire options for any length include:

  • #28 AWG SST Braided Type K
  • #28 AWG SST Braided alumel/alumel
  • 0.040’’ D Inconel sheathed Type K
  • 0.062’’ AWG SST Braided Type K

Or custom as required

Sensor Products – Wire Strain Gages

HITEC has more than 45 years of experience in the field of strain measurement, with a range of custom wire strain gage sensors from a variety of suppliers.

Strain Gages with Pre-Attached Leads

Pre-attached leads can be used to customize any type of strain gage using HITECs dedicated supplier. Pre-attachment of leads means soldering is not required, saving installation time and ensuring no errors are introduced.

Custom Weldable Strain Gages

Custom strain gages and temperature sensors for welding are available, in addition to high temperature systems, for applications in which clamping or curing cannot be used.

Weldable gages require only minimal surface preparations in order to be fitted and are environmentally protected because welding uses a spot-weld method.

This information has been sourced, reviewed and adapted from materials provided by HITEC Sensor Developments, Inc.

For more information on this source, please visit HITEC Sensor Developments, Inc.

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