DSH 725A Abnormal operation
http://decisions.iecee.org/icons/ecblank.gif DSH 725A
Abnormal operation
19.102(IEC 60335-2-6) 19.104(IEC 60335-2-9)
60335-2-6(ed.5) & 60335-2-9(ed.5)
Question:
In clauses 19.102 of IEC 60335-2-6:2002 and 19.104 of IEC 60335-2-9:2002, it is required to short-circuit the thermal control for the test. Note 5 of Sub-clause 19.1 of IEC 60335-1:2006 explains that instead of short-circuiting, controls may be rendered
inoperative.
In induction hobs, the thermal control of hob elements is normally a NTC controlled by the micro-controller. Short-circuit or open circuit of the NTC is easily detected by the micro-controller, but fixing the NTC in an intermediate value may not be detected.
IEC 60730-1:2007, Annex J has requirements for thermistors. There is a test for the drift of the R/T characteristic when the control is classified as Type 2.
Should the NTC be fixed at a specific value so as to render the thermal control inoperative? What is the condition required to be checked by clause 19.102?
Decision:
The NTC can be fixed to a specific value. This value must be in the middle of the operating range of the NTC, so as to avoid hysteresis problems that may happen towards the end of the range.
页:
[1]
