Input threshold AC minimum.
It is a read-write node.
The value of this node is 'OCTET STRING',
it is used to describe a float value.
So this string should fit the following rule:
1. This string should be terminated by '\0';
2. Every characters should be number or radix point;
3. The radix point should occur only once, and it should not
be the first or the last character of the string.
The value of this node should be smaller than 264.0V and larger than 90.0V.
And it should be smaller than the h3cPOEThresholdACMaximum.