Hello guys,
I have an issue about maximum cable length calculation of a digital input on Siemens SM321 card.
by calculation and according to tech data (Link at the bottom) :
Max cable resistance should be (24 VDC - 13 VDC) / 0.0042 = 2619 Ohms, 13 V and 4.2 mA being the minimum voltage and current @on state. If one consider some connection resistance (allowance) we can safely assume 2560 Ohms as maximum cable resistance. By using a 1.5 mm2 cable of 12.8 Ohms/km resistance, it turns out the maximum distance should be 2560/(2x12.8) = 100 Km.
In the other hand, by looking at the tech data , Siemens recommends max cable length of 1 Km only.
Could anyone explain please why this discrepancy (huge difference)
Thank you in advance
Link to Tech data : https://support.industry.siemens.com/cs/pd/46945?pdti=td&dl=en&pnid=13763&lc=en-WW
I have an issue about maximum cable length calculation of a digital input on Siemens SM321 card.
by calculation and according to tech data (Link at the bottom) :
Max cable resistance should be (24 VDC - 13 VDC) / 0.0042 = 2619 Ohms, 13 V and 4.2 mA being the minimum voltage and current @on state. If one consider some connection resistance (allowance) we can safely assume 2560 Ohms as maximum cable resistance. By using a 1.5 mm2 cable of 12.8 Ohms/km resistance, it turns out the maximum distance should be 2560/(2x12.8) = 100 Km.
In the other hand, by looking at the tech data , Siemens recommends max cable length of 1 Km only.
Could anyone explain please why this discrepancy (huge difference)
Thank you in advance
Link to Tech data : https://support.industry.siemens.com/cs/pd/46945?pdti=td&dl=en&pnid=13763&lc=en-WW