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Shunt Calibration Resistors 101

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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

 

 

Engaging Interface Calibration and Repair Services Expertise

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A high-quality load cell is a critical piece of technology for the design and testing of products throughout various, highly regulated industries including medical, aerospace and defense, automotive, and industrial automation. To get the most out of a load cell, just like anything else, you need to understand how to care for and maintain it. A poorly maintained load cell can lead to inaccurate data and poor performance.

Interface Calibration and Repair Services provide a valuable function for our customers in recalibration and technical support for the thousands of products manufactured by the leader in force measurement.  When cared for properly, a load cell should to be calibrated once a year or at least every two years under regular use. There are also certain circumstances where a load cell is damaged in use and needs immediate repair. Interface can handle calibration and repair of any load cell on the market, whether we build it or not.

A key differentiator for Interface is the fact that our calibration lab is ISO 17025 and A2LA accredited. These accreditations are typically for major calibration labs, not in a manufacturer’s facilities like ours. Our deep expertise in the development of load cells allows us to provide the highest quality calibration and repair services on the market because we know the product inside and out.

Interface’s Industry Leading Calibration and Repair Process

The Interface calibration team consists of 10 individuals dedicated to an optimized calibration and repair process that gets our customer’s load cells in and out as quickly as possible. The process begins with the front-end team, who manages the customer’s request, goes through the RMA process, and troubleshoots any additional concerns with the customer.

Once we review the product in-house at our Arizona headquarters, the load cell goes through a thorough inspection process to identify any necessary repairs and to ensure the load cell is in working condition for calibration. This includes an electrical test to evaluate if the load cell is in proper condition to calibrate. It’s also important to note that if the load cell can’t be repaired, there is no charge to the customer, and we work to find a replacement unit. The customer also approves any repairs that are necessary before work begins.

The final step in the process is the actual calibration. Our calibration team has many years of experience and know load cells inside and out. We also work with the most advanced equipment, including our proprietary Gold Standard® and Platinum Standard® systems. These devices ensure that the load cells are calibrated to the most accurate capability possible before returning to the customer. More information about Interface Calibration Systems can be found in our Calibration Systems 101 blog here.

Our commitment to building quality calibration systems is evident by the customers who also use them to do calibration in-house. In fact, in nearly every major manufacturing testing lab, you will find an Interface Gold Standard Calibration System and Gold or Platinum Standard Load Cells. This is because our customers are working on some of the most advanced hardware in their respective industries and fields. Engineers and testing labs trust Interface for accuracy, performance and quality.

Interface customers not only need to ensure their measurements are as accurate as possible to avoid product failure, they also need to prove the accuracy of their testing equipment for those products to pass inspection and make it to the market. We provide both our expert calibration services in our calibration lab, or through high-quality, high-reliability systems available that we build for our customers.

Interface Calibration and Repair Services

  • 50+ Years of Calibration Experience
  • Calibration of All Manufacturers Load Cells
  • 100,000+ Calibrations Performed Annually
  • Custom Calibrations
  • IPerform Service Software for RMA, Tracking and Permanent Archive of Test Data
  • NMI Certified Gold and Platinum Standard Reference Load Cells
  • Interface Gold Standard Calibration Software Used for Data Collection and Analysis
  • Full-Service Machine Shop for Mechanical Requirements

Force Capabilities:

  • NIST/NMI Traceable Calibration
  • 2 gf – 1 Million lbf Calibration Capability
  • (9) Hydraulic & (5) Deadweight Test Stands to Support Your Calibration Requirements

Torque Capabilities:

  • 0.022 – 100K in-lbf Capacities
  • NIST Traceable to 2.2K in-lbf
  • NMI Traceable 2.2K – 100K in-lbf

Interface calibration and repair services are designed with the customer in mind. Our process is fast, reliable and will ensure premium accuracy for our customer’s most complex and high-quality data-dependent design and test projects. Our team of experts work with every customer to ensure personalized world-class service.  It starts with engagement, how can we help?

For more information on Interface calibration and repair services, please visit /calibration-repair/.

Click here to schedule a service today.

Contributor:  Chris Brandenburg, Technical Services Manager at Interface