Performance specification and reference testing

BS 7908:1999 pdf free.Packaging – Temperature and time-temperature indicators- Performance specification and reference testing.
5.1 Temperature response and irreversibility test
5.1.1 Principle of test
Temperature indicators can produce an irreversible change if products have become either too hot, or too cold. To simplify this axid clause 6 of the stan(lard, all references will be ma(le to ifl(hcatorS that demonstrate a product has become too warm. The procedures are identical for indicators that show that a product has l)ecome too cold, except the temperature change is the reverse.
The test is designe(I to measure three key ProPerties of the Tis: the threshold temperature, the variation of the threshold temperature, and confirm the irreversibility of the indicator.
The TI is kept. in a constant temperature environment by placing it on a specially designed aiununiumu block in a constant temperature apparatus. The temperature is increased in steps, and time for (luilibrat ion is allowed at each new temperature until the device changes to its end-point. This is repeated with sufficient samples of TTIs that the mean and standard deviation of the threshold temperature can he obtained. Once the indicator has changed the temperature is then reversed to typical in-use temperatures to confirm irreversibility. The test. can be performed more quickly if more than one TI is placed in the aluminium block at one time, or more than one aluminium block is used.
5.1.2 Equipment
5.1.2.1 Constant temperature appa iv (us A constant, temperature environment shall be used which can maintain a set temperature with a maximum fluctuation of ± 0.1 °C in the aluminium block.
NOTE For tetuperat ures above 0°C, the apparatus may be a water bath or forced-air cabinet, but for temperatures below the freezing point of water, glycol or similar secondary refrigerant or a foreedair cabinet may be used.
5.1.2.2 A!uminiu,n blork
It. is important to Prevent any localized temperature gradients, and to do so, a suitably designed anodized soh(l aluminium l)Iock is used (see Figure A. 1 for an example). In this example, the TTI is placed in the well at the to!) of the block aiitl is covered and sealed L)y a 6 mm glass 11(1 and an “0” ring gasket; a temperature sensor is Placed Ill the hole located 10 mm below the well holding the device and penetrating to the centre of the block, and the temj)erature recor(led is taken as the temperature of the Tf I.
5.1.2.3 Tempera lure measuring system
The temperature sensor in 5.1.2.2 is connected to a read-out, specified in annex B.
5.1.3 Method
5.1.3.1 Determ i mit ion of threshold tempera litre
a) Store, handle and prepare (he device, according to the manufacturer’s instructions and maintain it in those conditions until immediately prior to using it in the test. Switch on the constant temperature apparatus and allow it to equilibrate at a temperature equal to three tinies the Class increment, below the manufacturer’s stated threshold I eniperat nrc and class. Place the aluminium block with the Lid removed into the constant temperature apparatus to equilibrate. Once the block has been equilibrated to the environment temperature, activate a TI in accordance with the manufacturer’s instructions and place in the well of the blocks and securely fasten the glass lid. Allow the TI to equilibrate the temperature of the block.
NOTE If preferred, the TI may be activated after placing it in the well of the block.
b) Increase the temperature of the apparatus in steps of 0.25 °C for (lass A devices, 0.5 °C for Class B devices, 2.5 °C and stabilize it for a time period of no less than 20 mm. Record the temperature at which the device changes colour to its normal end—point.
c) Confirm the TI class allocated by the manufacturer by calculating the mean standard deviation of the temperatures at which the TIs change.
NOTE The testing of each TI in lw sample may be simultaneous or consecutive.
5.1.3.2 IrreveiibiIity
After each determination of the threshold temperature, allow the teml)eralure of he apparatus to return to a temperature below the end point temperature, and (.0 equilibrate. Check the indicator to establish that. it has not altered from its end-point appearance before removal from the block well.
6 Reference testing procedure for time-temperature indicators
6.1 Critical reference temperatLire and irreversibility test for PHTTIs
6.1.1 Principle of test
The PHTTI is kept in a constant temperature environment by placing it in a suitably designed aluminium l)lock iii a constant temperature apparatus. The temperature is increased in steps and held at each new temperature for 24 h, if there is no response, or until a visible response (at least 5 % of the full TTI end-point) is observed. Five samples of the PH1’TIs are tested to enable the mean and standard deviation of the CRT to be obtained. Once a vIsiI)le response has been ol)talned the temperature is returned to typical in-use temperatures to confirm irreversibility.
6.1.2 Equipment
6.1.2.1 Consla iii tempera lure apparatus (see 5.1.2.1).
6.1.2.2 Alumin in in block (see 5.1.2.2).
6.1.2.3 Tern pera lure ineasu ring system (see 5.1.2.3).
6.1.3 Method
6.1.3.1 Determination qICRT
Store, handle and prepare the device according to manufacturers’ instructions and niaintain it in those conditions until immediately before use in the test.
Switch on the constant temperature environment and allow it to equilibrate at stated CRT minus 3 times the stated CRT tolerance. Remove the lid from the aluminium block and place the block into the constant temperature environment to equilibrate. Once the block has e(luihbrated to the environment temperature, activate a PIITTI, in accordance with the manufacturer’s instructions and immediately place it in the well of the block. Securely fasten the glass lid. The timing of the Tfl shall begin from the point of activation. The PHTTI shall be allowed to equilibrate to the temperature of the block and be held at that temperature for 24 hours.
NOTE If preferred, the ill may be activated after it is placed on the bkx’k.
Increase the temperature of the apparatus in steps of approximately 0.5 °C and leave at each successive temperature for 24 hours. Record the temperature at which a visil)le response (5 % of the full TTI end-point) is just detected.
Confirm that the recorded temperature at. which a V1SII)Ie CSI)OflSC is detected, is identical to the manufacturer’s stated value subject to the tolerance specified in Table 1.
NOTE The testing of each TI in the sample may be simultaneous or consecutive.
6.1.3.2 Irrerersibilitg
After each determination of the CRT allow the temperature of the apparatus to return to a temperature below the (‘RT and to equilibrate. The visible appearance of the device shall not have altered from its response.BS 7908 pdf free download.Performance specification and reference testing