Digital Outputs - Emerson FB2200 Instruction Manual

Emerson FB2200 Flow Computer Instruction Manual
D301784X012
March 2019
3.4

Digital Outputs

Depending upon how you ordered it, the FB2200 flow computer includes two, six, or ten channels
you can configure as digital outputs (DO), digital inputs (DI) or pulse inputs (PI).
Note
When using a digital output to drive an inductive load (such as a relay coil), place a suppression
diode across the load. This protects the DO from the reverse Electro-Motive Force (EMF) spike
generated when the inductive load is switched off.
When configured as digital outputs, the channels have the following characteristics:
Table 3-4. Digital Output Characteristics
Type
Digital
Output
(DO)
Note
Digital outputs are rated to 500mA maximum. In a small number of applications, however, the load
on the DO could have an effect on the uncertainty of the analog inputs and outputs. The typical
increase in uncertainty is around 0.05% and only occurs when all of the following are true:
Either of the two analog channels in the base I/O is used as an AI (in voltage mode) or as an AO
▪
and
Either of the two digital channels in the base I/O is used as a DO and
▪
▪ The total current load on these two DOs is greater than 300mA
Analog inputs in current mode and the I/O channels in the expansion I/O boards are not affected.
72
Number Supported
0 to 10 as follows:
▪ 1 or 2 non-isolated channels on CPU
module (DI/DO/PI1 and DI/DO/PI2).
Two are always present; you can
configure one, both, or neither as DOs.
▪ 1 to 4 additional isolated channels on
optional 8-channel expansion I/O
module (ISO DI/DO/PI3 to ISO
DI/DO/PI6). If module is present you
can configure one, two, three, four, or
none of the channels as DOs.
▪ 1 to 4 additional isolated channels on
optional 6-channel expansion I/O
module (ISO DI/DO/PI7 to ISO
DI/DO/PI10). If module is present you
can configure one, two, three, four, or
none of the channels as DOs. This
module is allowed only if 8-channel
expansion I/O module is also present.
Characteristics
DO is a low-side switch that sinks
▪
current to ground
Current rating of 500 mA
▪
▪ Maximum operating frequency of 50
Hz
▪ Pulse off/on time can be configured
with a 31 ms minimum on-time and a
31 ms minimum off-time
▪ Software-configurable with an output
state for initial power up and in the
case of a CPU failure
▪ Software-configurable failure mode of
fail-open, fail-closed, or hold-last-state
▪ When you configure a channel as a DO
it cannot be used as a DI or PI channel
I/O Configuration and Wiring