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Calibration Services - FAQ

 

Calibration Services - Frequently Asked Questions (FAQ):

 

FUTEK's A2LA and NIST accredited load cell calibration lab offers calibration and recalibration services for load cells, torque sensors, and strain gage amplifiers. FUTEK load cell calibration equipment are ISO 17025 and ANSI Z540-1 certified for high accuracy and fast turnaround.

How often should I get my sensor recalibrated?

As load cells are exposed to continuous usage, aging, output drift, overload and improper handling, FUTEK highly recommends a yearly recalibration interval. Frequent force sensor recalibration helps confirm whether the sensor maintained its accuracy over time and provides a load cell calibration certificate to show that the sensor still meets specifications.

However, when the sensor is used in critical applications and harsh environments, load cells may require even more frequent calibrations. Please consult with our Technical Support Team, who will help you evaluate the most economical calibration service interval for your force sensor.

How do I know if my sensor, or system, passed calibration?

A force sensor calibration must meet the sensor's non-linearity spec, which is found on the sensor's spec sheet. A system calibration, which is the calibration of a sensor and a digital instrument, must meet the sensor's non-linearity times two and is listed on a certificate as system tolerance. A note is added when a sensor, or system, does not meet the specifications.

Why should I do a complete system calibration?

A force measurement system usually encompasses the force sensor, instrument or signal conditioner (amplifier electronics), cabling, and connectors. A full system calibration ensures that the whole system is performing accurately as expected.

Choosing a complete system calibration allows you to start using your force measurement solution out of the box. A system calibration creates a plug & play solution where all connectors, cables, and instrument settings are taken care of.

What calibration service comes with my load cell or torque sensor?

It depends on the type of force sensor and what is specified on its spec sheet. Please refer to the sensor's spec sheet and look for the standard calibration specified and the loading direction (tension, compression, clockwise, counterclockwise) that is offered with the sensor.

I lost my certificate. How do I retrieve the calibration data?

Calibration summary information may be available online using the sensor's serial number. Please retrieve a summary of your sensor calibration data in our Online Calibration Tool here.

How do I convert the millivolt electrical output of my sensor into a load amount using the mV/V information on my calibration certificate?

Units of mV/V, or millivolt-per-volt, can be multiplied by the chosen supply voltage (or excitation voltage) to the sensor to get the mV output at the calibrated points. The slope of the curve of the calibration points is then used to convert the mV readings.

What is R.O.?

R.O. stands for rated output and will be the sensor's capacity, the last calibrated applied load, or the electrical equivalent of those points.

What is NL on my calibration certificate, and how it is calculated?

NL, or non-linearity, is how much the observed output under the load cell calibration curve deviates from a theoretical straight line, ranging from zero to the last calibrated loading point. The difference between these two points is displayed as a percentage of the final calibrated loaded amount, or rated output.

What does the zero mean on the table of the loading points?

The first zero reading is to eliminate any zero offset (or load cell zero balance) and allow the span from the loading to be presented.

What is shunt?

Shunt is a positive change in output that is generated from an unloaded sensor when resistance is placed between the -signal and- excitation connections of the sensor. Shunt information can be used to check the health of the sensor over time and assist with setting up devices, such as DAQ systems, by providing a known output without a physical load needed.

Why is converted shunt information shown for a negative direction, or dual directions, when the result of the shunt is positive?

Electrical shunt output is presented into an equivalent load amount using the slope of all directions calibrated. This supplies confirmation of what the shunt change will be if using either direction of the listed calibration information.

How do I use the A2LA equation to convert my sensor's output?

A2LA information is presented in a polynomial equation with applied load indicated with x and output indicated by y. The output is found by solving for y where the applied load is placed in the equation for x. The applied load is found by solving for x where the observed output is placed in the equation for y.

What is "as found"="as left"?

"As Found" information on a calibration certificate is the calibration specs of a force sensor, or system, as it was first received at our load cell calibration lab. "As left" information is the result after any noted adjustments that are made to help bring the sensor, or system, into the specification. "As found"="as left" means that the "as found" information meets specification and no adjustments were needed to the sensor or system.

I see both "as found" and "as left" data on my calibration certificate, was there an additional charge for this information?

An "as found" and "as left", if necessary, are performed under the same load cell calibration service and do not incur and additional charge.

Tension is offered standard with my sensor; can I order a compression and have both tension and compression?

Dual direction calibration must be performed at the same time and under the same environmental conditions and calibration setup to be effective. A dual-direction calibration service must be ordered to get valid dual-direction calibration information.

What should I send along with my force sensor?

Please include all cables that came with the sensor. If you are requiring a full system calibration, please include the instrument (load cell amplifier) alongside your sensor. We do ask that you remove all fixtures from the unit prior to shipment.

How long does recalibration take?

FUTEK's recalibrations typically take three or four business days upon receiving the unit. (If there are functionality issues, the turnaround time is around seven business days.) If you require expedited load cell recalibration, please contact our team and we will do our best to accommodate your schedule.

Did you know that FUTEK can perform on-site recalibrations?

Well, we can! Reach out directly to our Technical Support Team.

 

 

 


To get more information about load cell calibration, please visit our main Calibration Services Page. Ready to calibrate your Load Cell, Torque Sensor or Multi-Axis Force Sensor? Contact us to recalibrate your sensor.

 

Why is it important to calibrate load cell and torque sensors?

 

Load Cell Calibration Service is an adjustment or set of corrections that are performed on a load cell, or instrument (amplifier), to make that the sensor operates as accurately, or error-free, as possible. Every sensor is prone to measurement errors. These structural uncertainties are simply the algebraic difference between the value indicated by the sensor output versus the actual value of the measured variable, or, known reference loads, in order to generate the load cell calibration curve.

Every sensor is prone to measurement errors. These structural uncertainties are the simply algebraic difference between the value that is indicated by the sensor output versus the actual value of the measured variable, or known reference loads. Measurement errors can be caused by many factors:

  • Zero offset (or zero balance) — An offset means that the sensor output at zero load (true zero) is higher or lower than the ideal output. Additionally, zero stability relates to the degree to which the transducer maintains its zero balance with all environmental conditions and other variables remaining constant.
  • Linearity (or non-linearity) — Few force sensors have a completely linear characteristic curve, meaning that the output sensitivity (slope) changes at a different rate throughout the measurement range. Some are linear enough over the desired range and does not deviate from the straight line (theoretical), but some sensors require more complex calculations to linearize the output. So, load cell non-linearity is the maximum deviation of the actual calibration curve from an ideal straight line drawn between the no-load and rated load outputs, expressed as a percentage of the rated output.
  • Hysteresis — The maximum difference between transducer output readings for the same applied load; one reading is obtained by increasing the load from zero and the other by decreasing the load from the rated output. It usually measured at half rated output and expressed as a percentage of the rated output. Measurements should be taken as rapidly as possible to minimize creep.
  • Repeatability (or non-repeatability) — The maximum difference between transducer output readings for repeated loadings under identical loading and environmental conditions. It translates into the load cell's ability to maintain consistent output when identical loads are repeatedly applied.
  • Temperature Shift Span and Zero — The change in output and zero balance, respectively, due to a change in transducer temperature.
force sensor calibration force sensor recalibration
Figure 1: Force Sensor Calibration Curve.

 

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