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Understanding Cable Length and Temperature Effects

Interface offers several different accessories, from interconnect cables and mating connectors to base kits and TEDS. Cables and connectors are used to attach the sensor equipment to a multitude of components and systems including data acquisition systems, power amplifiers, test stands and other instruments.

Consideration of the cable and connectivity are important when selecting any transducer. Interface has several standard cable options based on the type of measurement device, the instrumentation, the pinout, type of connector and length required for the testing use case.

Find a range of all standard cable assembly options listed here, such as:

  • Interconnect Cable from Bayonet-Type Load Cell Connector to Pigtails, 10-foot in length
  • Amplified Load Cell Bayonet-Type Connector to Pigtails
  • Screw-type Load Cell (non-TEDS) Connector to Model 9860 Indicator 10-foot in length
  • Interconnect Cable from Model TS-type Torque Transducer to Pigtails, 10-foot in length
  • Interconnect Cable from Pigtails to Pigtails, 10-foot in length
  • Interconnect Cable from TX Torque Transducer 8-pin Connector to Pigtails, 6-meters in length
  • Interconnect Cable from Model WMC/2420/2430 Bayonet-type Load Cell Connector to Pigtails, 10-foot in length

Interface uses the highest grade mating connectors to ensure that the performance of your force and torque solutions are not compromised during use. We offer options for standard connectors based on the receptacle and plug type requirements, as well as custom solutions. Our mating connectors include:

  • Bayonet-Type Mating Connectors
  • Screw-Type Mating Connectors

Cable Length and Temperature Considerations

For high accuracy force measurement, the effects of the cable on the measurement must be considered for any testing program. For constant voltage excitation there are two significant effects:

  • An effect on the sensitivity due to voltage drops over the cable length.
  • An effect on the thermal span characteristics of the load cell due to the change of cable resistance with temperature.

If the Interface load cell is purchased with a cable of any length, the sensitivity is determined with the installed cable in calibration. Always consider your cable options when buying a new sensor.

TIP: For load cells with connectors, or if a cable is added that is not designed for the exact use, there will be a loss of sensitivity of approximately 0.37% per 10 feet of 28 gage cable and 0.09% per 10 feet of 22 gage cable. This error can be eliminated if a six wire cable is run to the end of the load cell cable or connector and used in conjunction with an indicator that has sense lead capability.

Since cable resistance is a function of temperature, the cable response to temperature change affects the thermal span characteristics of the load cell cable system. For 6-wire systems this effect is eliminated and is a non-issue in performance. For 4-wire cables the effect is compensated for in the standard cable lengths offered with the load cells if the load cell and cable are at the same temperature at the same time.

There are cables designed for hot temperature or corrosive environments that can not only withstand those conditions, but also provide accurate data despite environmental challenges.

TIP: For non-standard cable lengths, there will be an effect on thermal span performance. The effect of adding 10 feet of 28 gage cable is to cause a decrease in sensitivity with temperature equal to 0.0008%/°F. For an added 10 feet of 22 gage cable the effect is to decrease sensitivity by 0.0002%/°F. In some cases, it is tolerable to degrade performance since Interface standard specification is extremely tight. However, for long cable runs or high accuracy applications, this can be a significant factor. The best approach to eliminate the problem is to run six wires to the end of the standard cable length and sense the excitation voltage at that point.

Our customers in the oil and gas industry often need force measurement solutions that can perform under extreme heat and pressure, such as in a downhole application. The cables and connectors needed for this type of project often need custom braiding and coating to ensure the wiring will not melt or corrode in this environment. Read more in Interface Pressure Compensated Downhole Load Cell White Paper.

Interface also provides our maritime and off-shore testing customers with submersible solutions in which the connection between the submersible load cell and the connector must be sealed tightly to prevent water damage to the components.

We develop all our products and accessories using only components and materials that are engineered to perform for precision testing applications. Find all the accessories here. Our engineers will also work with your directly to find the accessories that fit your specific needs. If we do not currently offer the necessary connectors and cables in house, we can work with you to create a custom solution. We also provide a variety of options depending on the data requirements, whether it is permanent monitoring, as well as different cables based on instrumentation interconnectivity.

The best option is to always purchase the cable and any mating connector at the time you choose your load cell or torque transducer. This ensures it is calibrated with the cable and performs to the exact specifications as it was designed and guaranteed by Interface.

ADDITIONAL RESOURCES

Demystifying Specifications Webinar

Force Measurement Accessories 101

Accessories

Interface Guides

TEDS 101

Basics on Load Cell Base Kits

Mating Connectors

Interface Load Cell Field Guide

The Anatomy of a Load Cell

Have you ever stopped to think about what makes the things we use everyday work? At Interface, our engineers think about what makes up an Interface load cell on the production floor and in our design lab every day.

Whether we are manufacturing a new load cell or speaking to a customer about how it can help solve their test and measurement challenges, we are always thinking about what a load cell can do and how to perfect the process of building one that exceeds all customer expectations in performance, reliability and accuracy.

One thing that people ask us about all the time is, what does it look like inside the pioneering Interface blue load cell? In the photo below, you have a cross-section of a basic load cell identifying each of the components and how it all comes together to provide industries around the globe world-class force measurement solutions.

The first component to understand is the strain gage. This mechanism is embedded in the gage cavity and is a sensor that varies its resistance as it is stretched or compressed. When tension or compression is applied, the strain gage converts force, pressure, and weight into a change that can then be measured in the electrical resistance. You can read more in our recent strain gage 101 blog. Here at Interface, we manufacture our own strain gages in-house to ensure premium quality and accuracy.

The main features of a strain gage are illustrated in the following image:

  1. Grid Lines – strain sensitive pattern
  2. End Loops – provide creep compensation
  3. Solder Pads – used to solder interconnecting wire to the gage
  4. Fiducials – assist with the gage alignment
  5. Backing – insulates and supports foil and bonds the strain gage to the flexure

There are also multiple gage configurations depending on the type of load cell. These include:

  • Linear – measures the strain under bending (used in mini beam load cells)
  • Shear – measures strain under shear force (used in low-profile load cells)
  • Poisson – measures strain under normal stress (used in the Interface 2100 Series Column Load Cells)
  • Chevron – measures strain under torsion (used in the Interface 5400 Series Flange Load Cells)

The next component to understand is the load bearing component of the load cell. It is made up of the hub, diaphragm, outer ring, inner ring and base. This component deflects under load to allow the strain gages to send a signal through the connector to the data acquisition device. Customization can include changing the metal materials used to meet environmental or strength concerns and designing the beam height and thickness to meet certain size and stress considerations.

The mounting ring and connector are also incredibly important to the proper use of a load cell and accurate data collection. The mounting ring is the area in which the load cell is mounted to the test rig to measure force and collect data. It is important to pay attention to mounting instructions because an improperly mounted load cell can cause inaccurate results, as well as damage to the load cell. There are also mounting adapters available to fit a wide variety of test rigs.

The connector is the component that allows the load cell to connect to a data acquisition device. The connector is attached via a wire to the data acquisition device and force data is sent through this device to the user through ethernet or Bluetooth® depending on the load cell and data acquisition device configuration. Interface also sells a wide variety of data acquisition devices.

Load cells have many configurations and capacities. In fact, we have made tens of thousands of them over the years to meet standard, modified and engineered to order specifications. The load cell diagram above represents a popular low profile “pancake” load cell.  There are many other styles including miniature load cells, bending and dual bending beams, column-style, S-beam and load button load cells. However, even as the shapes and uses change, the anatomy remains relatively similar, with these main components acting as the workhorse of the load cell and providing accurate force data to the user.

For more information on Interface and our wide range of load cells, torque transducers and data acquisition devices check out our product categories on our site or download our product literature here.