Calibration


approximately 20 per cent, 40 per cent,, 60 per cent, and 80 per cent, of the range of two times the emission limit, and the test concentrations should be applied in a randomised sequence. After each change in concentration, the


first instrument reading shall be taken after at least three times the response time of the AMS, and at least three readings shall be made at each concentration. The time period between the star t of each of the three readings shall be separated by at least four times the response time.


There are two main linearity audit options:


1. Purchase bottles of pre-prepared and certified calibration gases for each of the required concentrations, or


2. Purchase a gas divider so that one certified bottle of calibration gas can be accurately diluted to create each of the required concentrations.


The first option can be particularly


expensive, and the number of bottles required can cause significant management and storage issues. The large number of gas bottles also creates greater potential for these costly purchases to run past their certified ‘use by’ date. Option 2 is therefore more popular because of its simplicity and lower cost. However, it is of course also necessary to be able to validate the gas divider… Most commercially available gas blenders


utilise mass flow controllers to manage the gases. However, they are not linear in response and therefore also need to be calibrated. For this reason, the Signal Group Model 821S Gas Divider does not use mass flow controllers. Instead, the 821S uses a manifold block with ten identical capillaries and a precision pressure balance regulator. A selector allows each of two gases (zero and calibration) to flow through these capillaries in ratios of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1 and 10:0. Consequently, including zero, it is possible to create 11 different equal increment concentrations for each calibration gas, with which to audit the gas analyser linearity. Since the design of the 821S provides


symmetrical increments, the procedure to check the accuracy of the gas divider is simple: connect the zero and calibration gas to the opposite connection and repeat the test. If the gas divider is operating correctly, the gas analyser will show exactly the same readings. In summary, a gas divider is an extremely


useful tool for checking and demonstrating the performance of gas analysers; minimising costs, simplifying procedures, and avoiding a forest of expensive gas bottles.


Signal Group www.signal-group.com Instrumentation Monthly September 2021


roller testing systems B


BeP euroPe uses HBK torque meters for tHe caliBration of


EP Europe in Bruges, a manufacturer of testing systems for assembly lines in the automotive industry,


utilises HBK’s range of HBM T40B torque meters and a TIM-PN measurement amplifier for the calibration of braking forces in new test benches. To minimise the error margin of the


measurement data as much as possible, BEP has defined a precise procedure for calibration/verification. The manufacturer of test benches uses the measured values of HBK’s torque meters as a reference value for the roller test benches. As part of Burke E. Porter (BEP) Group,


BEP Europe is one of the leading manufacturers of testing systems for assembly lines, that are supplied to the plants of practically all the well-known automotive brands. The testing systems are set up at the end of the production lines for the testing and adjustment of various vehicle parts and functions, including brakes, suspension and road handling. They adjust lighting, wheel alignment and test sensors for Advanced Driver Assistance Systems (ADAS), Adaptive Cruise Control (ACC), Head-up Display (HuD) and assisted parking. Frank Verschuere, supervisor of the


automation department within BEP says: “The roller test benches are equipped with four sets of rollers for four wheels, so that a car wheel sits between two rollers. Each set of rollers is driven by an electric motor. For each set we measure the force brought to bear by the electric motor on the car tyres, so that we can measure both the car’s power and the braking force. We


also have to take into account the mechanical frictional losses and electric losses in the electric motor.” The test benches and testing procedures


are developed according to the end customer’s specifications. For every test function a calibration procedure has been developed, to minimise the error margin of the measurement data as far as possible. Within the test benches the HBM torque meters are used for the calibration of braking forces. Since 2002 the T10F torque measurement readers and the MP60 measurement amplifier have also been used. Recently, BEP Europe switched over to the T40B and the TIM-PN measurement amplifier, which - used together - constitute a complete digital torque measurement system. HBK’s tools were chosen because of the data processing speed and accuracy of the HBM torque measurement sensors. “Every roller test bench is subject to


calibration after assembly and subsequently at periodic intervals,” says Yann Germain, technical quality manager at BEP Europe. “Once the measurements have been executed in accordance with the prescribed procedures, the torque measurement sensor is fitted onto the electric motors’ drive. By verifying and calibrating our measurements using a HBM sensor, we know whether the set measured values of our roller test benches fall within the tolerances. The testing systems are also re-calibrated if it turns out that deviations appear in the vehicles’ measurement results.”


HBK www.hbkworld.com 57


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