DSH 730 Abnormal operation and construction
http://decisions.iecee.org/icons/ecblank.gif DSH 730
Abnormal operation and construction
19.11.1/2/3/4 and 22.46
60335-1(ed.4);am1;am2
Question:
(1) In the construction shown in the figure, NTC1+micro+T1 operate as a thermostat for the heating element, R. The heating element does not have integral protection. During the application of the requirements in clause 19.11.2, transistor T1is shorted and NTC2+micro+T2 operates as a thermal cut-out to comply with sub-clause 19.13.
a.- Are NTC2+micro+T2 considered as a PEC?
b.- If so, are the clauses 19.11.3 (additional fault), 19.11.4 (immunity) and 22.46 (software classification) applicable?
c.- Considering that the thermostat software and the thermal cut-out software are separate parts of code, what software classes are applicable to the thermostat and the thermal cut-out?
(2) For the same construction, the manufacturer changes the parameters of NTC2 in such a way that NTC2+micro+T2 do not operate as a thermal cut-out but as redundant thermostat at the same temperature as the normal thermostat. Under the same conditions of the test in clause 19.11.2, short circuiting of T1, the heating element operates as in normal operation to comply with sub-clause 19.13.
d- Are the electronic circuit or some of its parts considered as a PEC?
e.- If so, are the clauses 19.11.3 (additional fault), 19.11.4 (immunity) and 22.46 (software classification) applicable?
f- Considering that the thermostats have separated software, what software classes are applicable?
Decision:
(1)
a- Yes
b- All sub-clauses are applicable
c- Taking into account that short circuit of T2 has to be considered in 19.11.2, then the thermostat is considered as a PEC too. Software class for T2 shall be at least B, and the software class for T1 is class A, B or C.
(2)
d- Yes, the temperature control of the circuit (T1+T2+micro+NTC1+NTC2)is considered as a PEC
e- All sub-clauses are applicable
f- Both software have to be class B
页:
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