GE 8121-DI-DC 16-channel DI, 24Vdc non-isolated
Power-up conditionsThe module uses the following values when it
powers up.
Module mode
Normal (not “failsafe”)
Active/inactive
All channels power up in the active state.
Alarms
All alarms are made inactive by having their
values set to high or low extremes, as appro priate.
Dead zone
0 (i.e. all changes of A/D data are reported for
an active channel)
Software filtering
Disabled
Channel type
Type K thermocouple or 3-wire RTD - Pt100
O/C sensor
Off
Visual indicators
CHANNEL “STATUS” LED (YELLOW)
On Sensor loop OK
Off Open circuit sensor and channel inactive
Flashing Open circuit sensor and channel active
OR Error condition
GENERAL
The 4–20 mA AO modules use a single D/A
converter in a sample-and-hold configura tion to drive each of the output channels. The
processor sets the current value for each of
the active channels once every 20 ms. Any
requested output values below 1mA are
clamped to 1mA to ensure that the open-loop
detection mechanism is always operable.
To verify that active output channels have
current flowing to the field, the processor
reads a hardware signal every time an output
is written to the D/A converter. If the signal
indicates “no current flowing”, i.e. < 1 mA, for
50 consecutive scans (i.e. one second), an
Open-Loop Detection failure is set for that
channel.

HART® capability
AO modules “with HART” are compatible
with all HART devices of protocol revision
5.0 or later. Each channel can communicate
with a single HART instrument and supports
HART communication with the wide range of
HART valve positioners now available. HART
universal command 3 can be used to gather
up to 4 dynamic HART variables such as
valve position, air pressure, etc., together with
HART status variables. These are scanned by
the BIM or Controller and may be communicated over the LAN for easy integration into
the control system. In addition, HART passthrough may be used for device configuration,
calibration and advanced diagnostics.
Data format
The output data has a resolution of 12 bits
but is stored as a 16-bit unsigned value. In
this range 0 is equivalent to 0mA and 65,535
is equivalent to 25mA.
MODULE OPERATING STATES
Failsafe mode
The module supports failsafe mode as
defined in the earlier I/O module introductory
section. When put in failsafe mode the output
can be made to adopt one of the following
options.
1) Use configured failsafe values
In this (default) mode, the module forces
the output to a predefined percentage
value. The default value is 0%.
2) Hold last value
In this mode the channel holds the last
value it output. When not in failsafe the
module adopts Normal mode.
Channel Active/Inactive
Each channel can be made active or inactive
individually. When a channel is made inactive
the output is disabled, i.e. deenergized.
When a channel is made Active again the
output is driven based upon the current
configuration.
Default/Power-up conditions
The module uses predefined values when
it powers up. The following parameters
summarize the state of the module when it
powers up.
Module mode:
Normal (not “failsafe”)
Active/inactive:
All channels power up in the Inactive state.
Visual indicators
CHANNEL “STATUS” LED (YELLOW)
On Field circuit OK
Off Open circuit field loop and channel
inactive
Flashing Open circuit field loop and channel active
OR Error condition
On the AO modules the yellow “Status”
LED reacts in the following way to module
conditions.
An error condition – i.e. a flashing LED –
could be as the result of the loss of the
HART communications signal.