Omron 3G3FV-PDRT1-SIN user manual Formulae, Left Side Equation

CompoBus/D Communications Line Design Chapter 2

Basically, in the CompoBus/D Network the permissible maximum voltage drop within the system can be specified at 5 V for a power supply line (+V or –V), by calculating the specifications for the voltage of the communications power supply (24 VDC) and the input voltage of the communications power supply of each device (11 to 25 VDC).

Of the permissible 5-V maximum voltage drop within the system, the permissible voltage drop is 4.65 V in the trunk lines and 0.35 V in the drop lines.

The following formulae are applicable when power is supplied independently for communications and the internal circuit. For details on voltage drop and formulae when the communications power supply and internal circuit power supply are shared, refer to the CompoBus/D (DeviceNet) Opera- tion Manual.

HFormulae

Try to calculate the best location for each node using the formula below. If the best location for each node can be determined using the formula, the specifications for the power supply to each node can also be met. Do not exceed the maximum current capacity of the cable (Thick Cable: 8 A and Thin Cable: 3 A).

{(L1 ⋅ RC + N1 ⋅ 0.005) ⋅ l1} + {(L2 ⋅ RC + N2 ⋅ 0.005) ⋅ l2} + ..... + {(Ln ⋅ RC + Nn ⋅ 0.005) ⋅ ln} x 4.65 V

Li:	The distance (m) of the trunk line between the power supply and node i.
Rc:	Maximum cable resistance for approx. 1 m
	(Thick Cable: 0.015 Ω /m, Thin Cable: 0.069 Ω /m)
Ni:	The number of T-branch Taps on the trunk line between the power supply and node i.
Ii:	The consumption current required for the communications power supply for node i.

0.005 Ω = The contact resistance of the T-branch Taps.

Note If there are nodes on both sides of the power supply, the formula is used to calculate the best location in each direction, and if the conditions are satisfied, then the locations are valid. The conditions are satisfied if the following equations are true.

Voltage drop (V) on trunk line at left side x 4.65 V

Voltage drop (V) on trunk line at right side x 4.65 V

DCalculation Example

Terminating Resistor	Trunk line	Trunk line	Terminating Resistor
	(5-wire cable)	(5-wire cable)

3 m max.

Node	Node	Node	Communications		Node	Node	Node
			power supply
0.1 A	0.25 A	0.2 A			0.15 A	0.25 A	0.15 A
	40 m	40 m	40 m	40 m	40 m		40 m

Left Side Equation

Node 1:	(120	0.015 + 3	0.005) 0.1		= 0.1815	(V)
Node 2:	(80	0.015 + 2	0.005)	0.25	= 0.3025	(V)
Node 3:	(40	0.015 + 1	0.005)	0.2 = 0.121 (V)

If 0.1815 + 0.3025 + 0.121 = 0.605 V x 4.65 V, the conditions are satisfied.

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