7866 Digital Controller - Honeywell 7866 Operation And Maintenance Manual

Introduction
1.3

7866 Digital Controller

The 7866 Digital Controller shown in Figure 1-3 can provide a current output, a digital display of the
measured gas percentage, and up to two alarm circuits. The alarm limits are set using the integral keyboard
on the face of the instrument. The SETPOINT SELECT key is used to select the appropriate range.
A second current output is available and will supply a value for the selected range data that can be
retransmitted to a remote indicator.
The unit also provides access to the calibration settings for each range. The zero and span settings are
entered using the group prompt CALIB, function prompt RANGE n (n = 1, 2, or 3). Zero and span are
"live" readings until the FUNCTION key is pressed, at which time that displayed value is captured. The
increment/decrement keys can then be used to change the desired value. These values are normally secured
from inadvertent or unauthorized tampering using a four-digit security code.
If alarms are in use, the 7866 Digital Controller displays the alarm status. The alarms are listed by number
next to the ALM annunciator on the left side of the display.
If the Alarm is in force, the number "1" or "2 " will be lit indicating the respective alarm and process
violation. These alarms will de-energize output relays that the user may hardwire to annunciation circuits
or to a safety shutdown system depending on the application. Alarm limits are adjusted through the group
prompt SETUP, function prompt ALARMS. The security feature can also secure alarm limits.
Normal power losses, even over extended time periods, will not affect the configuration of the controller.
The controller uses a nonvolatile memory system to secure the controller's current configuration and
calibration settings. This will prevent any loss during outages.
The factory calibration constants that can be used with the controller are stored in its nonvolatile memory.
If a field calibration is lost, you can quickly restore the "factory calibration" and overwrite any previous
field calibration. Protection after calibration is available through the LOCKOUT feature.
The controller's circuit boards are accessible for service and replacement. The modular design permits
selective replacement of circuits as required. The removable chassis eliminates the need to remove or
change any field wiring for a circuit board or controller change.
The rear of the controller has three terminal strips for field wire termination. All field terminations are
accessible from the rear of the controller. Stranded wire of 20 to 22 gauge is recommended. See wiring
section for more specific instructions.
The 7866 Digital Controller features a universal power supply that can be connected to line voltages of
90 Vac to 264 Vac or 24 Vac/dc. The line frequency can be 50 hertz or 60 hertz.
Power for the 7866 Sensing Unit is supplied by a separate 30 Volt dc power supply. This power supply is
also utilized by the controller to power its interconnections with the sensing unit.
4 7866 Triple Range Digital H and CO Analyzer/Indicator - Operation and Maintenance
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