Power Consumption Calculation; Determining I/O Channel Power Consumption - Emerson Fisher FLOBOSS 407 Instruction Manual

FloBoss 407 Instruction Manual

1.5 POWER CONSUMPTION CALCULATION

A ROC/FloBoss system's power consumption determines power supply and battery sizing for both line
and solar power supplies. Table 1-1 and Table 1-2 provide information to assist in determining power
requirements. For non-analog I/O, size the I/O module scaling resistors (see Section 3) for optimal
current to minimize current drain on the power supply.

1.5.1 Determining I/O Channel Power Consumption

In estimating total I/O power requirements, the "duty cycle" of each I/O channel (built-in I/O or
modular I/O) must be estimated. For a non-analog I/O channel, the duty cycle is essentially the
percentage of time that the I/O channel is active (maximum power consumption). For example, if a
discrete output is active for 15 seconds out of every 60 seconds, the duty cycle is:
Duty Cycle = Active time/(Active time + Inactive time) = 15 sec/60 sec = 0.25
For an analog I/O channel, the duty cycle is approximated by estimating the percentage of time the
channel spends in the upper half of its range (span) of operation. For example, if an analog input wired
as a current loop (4 to 20 mA) device operates in the upper half of its range 75% of the time, then 0.75
would be used as the duty cycle. If the analog channel generally operates around the midpoint of its
span, use 0.5 as the duty cycle.
To calculate the total power consumed by an I/O channel, first select either the 12 or 24 volt column in
Table 1-1 or Table 1-2. Then, read the minimum (P
from the table for the desired I/O channel. Use the following equation to calculate the power
consumption for a channel with the duty cycle taken into account:
Power = (P
max
Multiply this value by the quantity (Qty) of I/O channels with the same duty cycle and enter the
calculated value in the Subtotal column. Repeat the procedure for all other I/O channels used. For a
FloBoss 407, total the values in the Subtotal column in Table 1-2, and enter the value in the I/O
Modules row of Table 1-1.
Rev 5/00
x Duty Cycle) + [P
min
) and maximum (P
min
(1 - Duty Cycle)]
) power consumption value
max
1-9