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Shunt Calibration Resistors 101

Shunt calibration is a process of calibrating a measurement instrument using a shunt calibration resistor. The shunt calibration resistor is connected in parallel with the measurement instrument to provide a known resistance value, which is used to calculate the instrument’s accuracy.

In shunt calibration, a known current is passed through the shunt calibration (cal) resistor, which generates a known voltage drop across the resistor. This voltage drop is measured using the measurement instrument being calibrated, and the instrument’s accuracy is calculated based on the known resistance value of the shunt calibration resistor and the measured voltage drop. They create a simulation of load and verify the health of the sensor. Commonly, they are used to scale instruments.

The accuracy of the measurement instrument can be calculated by knowing the shunt resistor’s precision level and applying Ohm’s Law, which states that the current passing through a resistor is proportional to the voltage drop across it and inversely proportional to its resistance value.

Shunt calibration can be used to calibrate force measurement devices, including load cells. Interface provides shunt calibration resistors in our accessories line as “loose” resistors. They are also available with engineered to order requests for designs into cables, connectors and even within the load cell.

Shunt calibration is an important process for ensuring accurate and reliable measurements in various industrial, commercial, and scientific applications. It allows measurement instruments to be calibrated quickly and cost-effectively, and it improves the accuracy and reliability of the measurement data.

What is a shunt calibration resistor?

A shunt calibration resistor is a resistor that is connected in parallel with a measurement instrument to provide a known resistance value. The purpose of the shunt calibration resistor is to calibrate the instrument to accurately measure the current passing through it. Shunt calibration resistors are often used with load cells to improve the accuracy and reliability of their measurements.

How are shunt calibration resistors used with load cells?

Load cells typically generate a small electrical signal in response to applied force or weight. This signal is amplified and processed by a signal conditioning circuit before a data acquisition system or controller uses it. The signal conditioning circuit can utilize an internal shunt calibration resistor on the instrumentation side, or activate a resistor located upstream in the system.

Shunt calibration resistors located either in the sensor, cable, or instrument will be switched into the circuit during the shunt calibration process, shunting and diverting current in the process. This shunting effect unbalances the Wheatstone bridge, simulating loaded output from the sensor. Because the resistance value is known, sensor span output and thus instrument scaling can be accurately verified. This electrical simulated signal negates the need for physical force or torque calibration of the system.

The shunt calibration resistor provides a known resistance value, which is used to verify the health and output of the load cell, ensuring accurate system measurement of the applied force or weight. The resistor diverts a small portion of the load cell’s excitation current. The value of the shunt calibration resistor is carefully selected based on the load cell’s characteristics and the desired measurement accuracy.

Shunt calibration uses the shunt resistor to force a load cell bridge to provide a fake signal output. It allows one to check for sensor health and whether the signal behavior has deviated from an original calibration certification with initial shunt output data.

This forced signal output allows for the attached instrument to be scaled. This could be setting signal conditioner scaling:  When the load cell reaches max calibrated force, is the mV/V input properly scaled for the exact 5V, 10V or 20mA conditioner output? The other setting option is displayed units of measurement on a display: Is the load cell’s calibrated 3.999mV/V output at 100 lbs displaying 100 lbs on the display?

Shunt resistors are sized by resistance value to provide approximately two-thirds or three-quarters full scale output signal. Having this recorded value on the calibration certification the instruments can be scaled as necessary for full scale, and future shunt checks can ensure nothing is changing with the health of the circuit.

Interface Shunt Calibration Resistors – RCAL Resistors

Interface shunt calibration resistors, known as RCAL Resistors, are an accessory product. They are made from the highest components and processes to ensure the specifications for your Interface products perform to meet their published specifications. Available RCAL Models include RS-100-30K, RS-100-40K, RS-100-60K, and RS-100-120K are available.

Interface RCAL Resistors are high precision components and provide an effective, method for checking the calibration of a load cell system in the field or when a means of applying actual forces is unavailable.

  • Designed to work with Interface products.
  • Made with the highest quality components.
  • Created to maintain the specification of the product.
  • Precision wire-wound
  • 5 ppm/°C, 0.01%

U.S. dimensions and capacities are provided for conversion only. Standard product has metric capacities and dimensions. U.S. capacities available upon special request and at an additional cost.

What are the benefits of using shunt calibration resistors?

There are several benefits of using shunt calibration resistors in measurement applications:

  • Calibration: Shunt calibration resistors can be used to scale measurement instruments, ensuring that they provide accurate calibrated unit readings. Shunt calibration can often substitute the need for physical force or torque system calibration
  • Convenience: Shunt calibration can provide a quick and easy system health check either before or immediately after a test. Confirming stable and consistent shunt readings can ensure data integrity in between regular scheduled physical calibration intervals.
  • Cost-effective: Using a shunt calibration resistor is an inexpensive one time investment vs time and cost associated with pre or posttest physical calibrations. This brings the freedom for frequent and quick system calibration checks with minimal equipment down time.
  • Flexibility: Shunt calibration resistors can be used with a wide range of measurement instruments, allowing for greater flexibility in measurement applications. Additionally, many instruments allow shunt resistors to be interchangeable for support of varying sensor outputs.

Overall, shunt calibration resistors are a practical and convenient alternative to physical system calibrations. Shunt calibration resistors can be packaged into all Interface load cells with support across most of the available instrumentation as well. Frequent system health and signal stability checks are vital to ensuring consistent integrity with test data and shunt calibration resistors bring such empowerment for extraordinarily little initial investment.

Contributor: Brian Peters

Additional Resources

Metrologists and Calibration Technicians 101

System Level Calibration Validates Accuracy and Performance

Shunt Calibration for Dummies – Reference Guide

Shunt Calibration 101

Regular Calibration Service Maintains Load Cell Accuracy

Top Five Reasons Why Calibration Matters

 

 

TEDS 101

In the electronics industry, sensor compatibility challenges can lead to significant issues with efficiency, accuracy, safety and more. When it comes to force measurement sensors, incompatibility issues can railroad an entire project.  This is where the role of Transducer Electronic Data Sheets (TEDS) comes into play.

TEDS is a set of electronic data in a standardized format stored in a chip that is attached to a transducer, therefore allowing the transducer to identify and describe itself to the network and ease automatic system configuration. This self-identification capability for the transducer is needed for maintenance, diagnostics, and to determine mean time between failure characteristics. The chip stores information such as manufacturer name, identification number, type of device, serial number, as well as calibration data. The TEDS can be uploaded to the system upon power up or request. It also serves as documentation for the transducer.

Transducer Electronic Data Sheets (TEDS) provide:

  • Sensor with electronic identification
  • IEEE 1451.4 standard for smart transducer interface
  • Plug and play readiness
  • Storage of sensor information and calibration data
  • Use with new or existing sensors

IEEE1451.4 specifies a table of identifying parameters that are stored in the load cell in the form of a TEDS. TEDS is a table of parameters that identify the transducer and is held in the transducer on a EEPROM for interrogation by external electronics.

A TEDS chip becomes the ultimate tool to allow users to take off-the-shelf sensor solutions and integrate them into a total force measurement solution. The key benefits TEDS provide includes:

  • Eliminating potential for data entry error
  • Simplifying new system setup and speeds up the process
  • Making swapping load cells in and out of a test system seamless
  • Improving safety by ensuring the system has the correct sensors
  • Easily identifying and tagging sensor locations
  • Improving inventory control of sensors
  • Changing sensors out without jeopardizing integrity of the system

TEDS chips can be sold separately or integrated into existing systems such as instrumentation products. Interface offers both options, selling TEDS as a standalone accessory, as well as integrating them into instrumentation solutions, such as:

9840 Calibration Grade Multi-Channel Load Cell Indicator

Model 9840 is suitable for use in calibration labs, field service, or anywhere high accuracy is important. This product’s features include a bipolar 6-digit 2-line display, remote sense, low noise, 24-bit internal resolution, USB port with RS232 communication, mV/V calibration, store calibrations for up to 25 sensors. 6-point linearization, unit conversion and front-panel tare. This unit also has Self-calibration via TEDS Plug and Play ready IEEE 1451.4 compliance.

9320 Battery Powered Portable Load Cell Indicator

Model 9320 is a bipolar 7-digit handheld meter featuring two independently scalable ranges, peak and valley monitoring, display hold, mV/V calibration, and a power save feature. Typical battery life exceeds 45 hours of continuous use and 450 in low power mode. IEEE1451.4 TEDS Plug and Play compliant.

Additional TEDS Ready Interface Solutions

9840-400-1-T 4-Channel Intelligent Indicator

9840TQ mV/V Input Torque Transducer Indicator

9870 High-Speed High Performance Teds Ready Indicator

BX6-BT Portable 6-Channel High Speed Bluetooth Data Logger

BX8-AS BlueDAQ Series Data Acquisition System With Industrial Enclosure

BX8-HD15 BlueDAQ Series Data Acquisition System For Discreet Sensors With Lab Enclosure

BX8-HD44 BlueDAQ Series Data Acquisition System For Multi-Axis Sensors With Lab Enclosure

These solutions make a great addition to any testing environment as they enable quick compatibility and are very easy to setup. To learn more about TEDS or to explore how TEDS can help solve your force measurement challenges, contact us to explore the possibilities.