BS ISO 7524:2020 pdf download.Ferronickels — Determination of carbon content — Infrared absorption method after induction furnace combustion.
8.2 Blank test and zero adjustment
8.2.1 Carbon contents ≤ 0,1 % For each instrument range, transfer the selected mass of flux (5.5.2), to the nearest 0,005 g, into a pre‑ ignited crucible (6.2), add the selected mass of a CRM (5.6) having a very low carbon content, and then cover it with the selected mass of accelerator (5.5.3). The type and mass of the flux and accelerator used in the blank test should accord with those used for determinations (details as in 8.4.1). Record the mass of the CRM. Place the crucible and contents on the furnace pedestal and operate the furnace in accordance with the manufacturer’s instructions. Repeat the determination three more times. Average the results. Subtract the carbon content of the CRM from the average to determine the blank value. If the blank is greater than 0,001 % (mass fraction) and the related standard deviation is greater than 0,000 2 % (mass fraction), find the cause of the problem, fix it and repeat the experiment. Record the average blank value into the analyser in accordance with the manufacturer’s instructions. NOTE 1 The reading obtained corresponds to the blank due to the crucible, flux and accelerator. If the analyser does not have automatic blank correction, the blank value should be subtracted from the total result prior to any calculation. NOTE 2 An alternative procedure is to record the reading of the blank test and make the correction using a calibration graph.
8.2.2 Carbon contents >? 0,1 % It is preferable not to carry out a blank correction. However, a check of the blank level shall be done. The value shall remain below 0,001 % (mass fraction).
8.3 Calibration
8.3.1 Select a set of steel and/or ferronickel CRMs (5.6) for calibration and verification which, at a minimum, fall at the bottom, top and quartile points of each operational operating range.
8.3.2 If the instrument has more than one carbon detector (measurement system), carry out the adjustment described in this section on each one. Establish all experimental parameters for each range of carbon. Parameters to be specified include: — crucible: to be pre‑burned or not; — flux and accelerator: type and mass; — test portion: mass.
8.3.3 For each detector (see 8.3.2) weigh an appropriate amount (usually 0,50 g) of a CRM having a carbon content corresponding to the top of each operating range into a pre‑ignited crucible (6.2). Add the pre-selected amounts of flux (5.5.2) and accelerator (5.5.3) and combust as described in 8.4.1. Repeat this process twice. If the results are situated in the interval “Certified Value ± 2σ”, adjust the net instrument reading to correspond to the certified content of carbon in the reference material, according to the manufacturer’s instructions.
8.3.4 Check the linearity of the calibration by analysing at least three times a CRM having a carbon content in the middle of the range of the detector. The result shall be situated in the interval “Certified Value ± 2σ”. Correct any non‑compliant conditions before continuing to the next step.BS ISO 7524 pdf download.