AS 2985:2009 – Workplace atmospheres—Method for sampling and gravimetric determination of respirable dust.
6 and 7.) Some pumps may require pulsation dampers to achieve this performance. Pumps shall be lined with automatic flow control facilities.
6.$ Secondary- flowmctcr
A flowmeter or an secondary- device such as a rolameter or electronic flowmeter shall be calibrated against the primary flowmctcr as set out in Appendix I-I. The secondary flosvmeter shill be used to measure (he flow rate of the sampling train immediately before and after sampling. The secondary tlowmeter shall be re-calibrated whenever it is to be operated under conditions substantially different from those of the previous calibration For example—
(a) when sampling and/or flow rate determination is conducted at an altitude ditTering by more than 500 rn or at a temperature differing by more than 15°C from that at the previous calibration: or
(b) when experience indicates such re-calibration is necessary due to stability and maintenance hisior of the flow meter.
I Ii is generally not possible to simply c.ileulate the dilTerent how ritcs that will inevitably result from a change of conditions such as those given above,
2 Rotameters can give incorrect readings due to sticking of the float, high humidity and use in a non-vertical position, or under conditions of vibration
3 Errors can occur using electronic tlowmetcr due to adverse cnvironmcntal conditions.
6.6 Timing device
A stopwatch or other timing device capable of measuring elapsed lime within 1% of true elapsed time.
6.7 ytierobalanec
6.7.1 Gen
A five-place microbalance with a scale division of 10 ag or six-place microbalance with a scale division of I pg. A standard laboratory four-place analytical balance is not suitable for this application.
6.7.2 Mkrobulance caithraiion
The following requirements and recommendations apply:
(a) The microbalance shall be calibrated every three ycars. using the following principles, by either—
(i) a suitable accredited testing au(horily: or
(ii) competent staff empIoyin test methods as described by Morris and Fen.
(b) Tests for departure from nominal linearity shall be conducted for at least 5 and preferably 10 points from icro up to not more than 50 or 100 mg. If the measured departure from nominal linearity exceeds the expanded uncertainty of the reference weights, the balance should be serviced, or appropriate corrections should be made.
(c) Hysteresis and, where applicable, oft—centre pan loading shall be conducted using a weight in the range of SOlo 100 mg. Any hysteresis and off-centre effects greater than the scale of the balance should be rectified by servicing, or by an appropriate change in operating procedures.
(d) Repeatability tests on the microbalance shall be conducted with a weight not smaller than around the working range used for weighing filters, and not greater than 50 rng. esery si months. e.g. in accordance with Morris and Fen.
(e) A limit of performance shall be calculated wheneser a full calibration of the balance
is performed.
6.11 Static eliminator
Suitable instruments for eliminating static include the following, an> of which may be used:
(a) an ionising electrode static elimination bar or I -shaped electrode:
(b) a high voltage corona discharge device: or
(c) a positive ion or an alpha particle source ionizing unit (Americium 241 of0.4 to 4 MBq actisity or Polonium 210 of 20 MHq activity). The Po unit should be renewed when found to be ineffectise (i.e. generally every one to two years). Both units will require a government licence to operate/dispose of them.
The sampling pump batter>’ should be re-charged or the dry cells replaced and. if necessary. the pump should be run for up to 15 mm in a clean atmosphere immediately before flow rate determination. It is advisable to stabilize the flow rate through a warnl-up’ sampler, which is not otherwise used. e.g. in calibration to reduce the risk of contamination. Some auroniatic flow control pumps require little or no settling-in period.
The pump flow rate should be adjusted accurately to the designated flow rate (see Table 2) using a calibrated flowmctcr (see Clause 6.5). Immediately prior to determining the flow rate, disconnect the warm-up sampler and connect the sampling train to be used in the field.
The calibration equipment and technique should be of such accurac>’ that the flow rate can he measured to within ±5%.