ROC364 Instruction Manual
1-8 General Information Rev Jun/05
Table 1-2. Power Consumption of the I/O Modules
Power Consumption (mW)
12 Volt 24 Volt
I/O Module
P
min
P
max
2
P
min
P
max
2
QTY
Duty
Cycle
1
Sub-
Total
(mW)
AI Loop 170 495 170 495
AI Differential 75 75 75 75
AI Source 110 305 130 470
AO Source 145 585 145 585
RTD Input: P
min
is at –50°C
(–58°F); P
max
is at 100°C (212°F)
240 475 475 930
DI Isolated 1 10 1 10
DI Source 1 55 1 205
PI Isolated 1 30 1 30
PI Source 1 70 1 230
Low Level PI 1 45 1 45
SPI Isolated 1 10 1 10
SPI Source 1 55 1 205
DO Isolated 1 25 1 25
DO Source (P
max
is at 57 mA) 30 815 30 1585
DO Relay 12 Volts 20 420 N/A N/A
DO Relay 24 Volts N/A N/A 20 470
HART Interface Module 85 685 85 1285
I/O MODULES TOTAL
NOTES: 1. For analog I/O channels, the Duty Cycle is the percent of time spent in the upper half of the
operating range.
2. The P
max
amount includes any power drawn by a ROC-powered field device such as a
transmitter.
1.5.2 Determining Radio Power Consumption
In determining power requirements for radios:
1. Estimate the Duty Cycle for the radio.
The Duty Cycle is the percentage of time the radio is transmitting (TX). For example, if a radio
is transmitting 1 second out of every 60 seconds, and for the remaining 59 seconds the radio is
drawing receive (RX) power, the Duty Cycle is:
Duty Cycle = TX time ÷ (TX time + RX time) = 1 sec ÷ 60 sec = 0.0167
2. Calculate the total power consumed by a radio, obtain the power (P) consumption values for
transmit and receive from the radio manufacturer’s literature, then use the following equation to
calculate the power consumption for a particular Duty Cycle:
Power = (P
TX
x Duty Cycle) + [P
RX
(1 – Duty Cycle)]
3. Determine the power consumption for all radios that use power from the ROC, and enter the total
calculated value in the Sub-Total column in Table 1-1.
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