My customer has question about ISO1211 formula. Below is IEC 61131-2 type-1 standard. For type 1, the turning point is 15V between VIH and VIL. If use our below formula, VIH is not equal to VIL. If customer want to use 15V, what's formula we can use?
VIH (15V) = 8.25 + Rthr * 2.25mA*562 / 562 >> Rthr is 3Kohm.
If we input 3Kohm in to VIL formula, we can't get 15V. Which formula we can use?