Operating Modes - Hoffman Controls 890-DSQ Series Complete Installation & Operating Instructions

Operating Methods Con't
IMPORTANT:
After updating any information displayed on the
LCD's screen, the installer MUST review ALL of
the 890-DSQ Sequencer's mode, menu, submenu
and numerical value options to 1) ensure that all
of the operating parameters, needed for the appli-
cation, have been correctly selected and 2) also
ensure that any unneeded or undesired options or
numerical values have not inadvertently been left
REMOTE OPERATION
Remote operation is accomplished by using a Modbus RTU
master computer to communicate with the 890-DSQ Sequencer
via the Modbus 3 wire connection. (The third wire is a common
ground reference). During remote operation, the Modbus RTU
master computer can read the information stored in 75 of the 890-
DSQ Sequencer's 76 internal registers (Register 72 is a write only
register). Refer to Tables 2A & 2B (pages 16 & 17) for a complete
list of the registers, by number, and the required data range
allowed for each register. The Modbus RTU master computer can
also write information to 65 of the 76 sequencer's internal registers
(Registers 0-57 & 68-75). Registers 58 thru 67 are read only regis-
ters and therefore ignore any data written to them (see Modbus
Operation section on pages 18).
IMPORTANT:
If any of the down loaded Modbus data is incor-
rect, the 890-DSQ Sequencer's microcontroller
will change the incorrect data into software
selected default values during the sequencer's next
operating cycle. Therefore, after updating any
data remotely, the operator MUST allow the 890-
DSQ Sequencer to operate over its entire expected
range (°F, PSI or VDC) before reviewing ALL of
the data contained in each of the sequencer's 76
register addresses to 1) ensure that all of the oper-
ating parameters and numerical values, needed
for the application, have been correctly selected
and 2) also ensure that any unneeded or undesired
options or numerical values have not inadvertently
been left selected.
The Modbus RTU master control can only write data
to 27 of the 890-DSQ Sequencer's registers at a time,
and read data from 29 registers at a time, due to buffer
size limitations in the sequencer's microcontroller.
selected.
NOTE:

Operating Modes

The following information is provided to identify and explain
the 890-DSQ Sequencer's operational modes, menus, submenus,
and numerical value options. The sequencer's MODE button
is used to sequentially cycle thru the seven (7) available modes
displayed on the sequencer's LCD screen. Pressing the MODE
button an eighth time returns the LCD to the Home Screen.
An 890-DSQ Operating Modes Chart (Figure 3, pages 10 &
11) is provided to allow the operator to track his/her progress thru
the various LCD's screens. The Operating Modes Chart's informa-
tion is viewed starting from the Home Screen, located at the top
center of the Operating Modes Chart, and continuing counter
clockwise (to the left) around the chart.
NOTE:
The Figure 3, 890-DSQ Operating Modes Chart, (on
pages 10 & 11) information is presented in the same mode, menu
and submenu order as the information presented on the LCD
screen, when following the chart's information in a counter clock-
wise direction (to the left). Press the MODE button to begin.
MODE 1: To Test Fans Press Enter.
The contactor wiring and condenser fan or heating element
wiring, connected to each relay output, can be sequentially
tested in this mode, by pressing the UP and DOWN buttons.
Pressing the UP button turns on the next stage, while pressing
the DOWN button turns off the last stage, that is currently on.
MODE 2: Change output stage settings.
The output stage settings can be changed from the pre-
programed stage options, by pressing the ENTER button when
the above screen appears on the LCD. The LCD screen sequence's
through the following 4 menu screens with each press of the
ENTER button:
1) Is Variable Stage Used? No
The (VS) variable stage is used (activated) when continuously
smooth airflow thru a condenser, or continuously variable current
flow thru a heating system, is desired. Implementing the VS option
requires connecting the sequencer's VDC and/or PWM output(s),
to external SCRs, rated at twice the current capacity of the largest
heating coil, or continuously variable speed EC motors. Press the
UP or DOWN button to change the No to a Yes or vice versa.
Then press the ENTER button to save the correct answer and
advance to the LCD screen below.
2) Variable Stage Ratio: 1.0
Is Variable Stage Used?
When the
this screen will appear. The variable stage ratio is used to set the
ratio of the total variable stage capacity to that of a single fixed
stage. In order to provide continuously smooth operation when
using hysteresis, the ratio should be greater than 1.
This unique 890-DSQ feature provides PWM and VDC outputs
that are used to drive variable speed EC motor fans or SCRs. When
the variable speed fans or SCRs are present, the sequencer intel-
ligently modifies the output to the variable speed fans or SCRs so
that, as additional fixed speed fans or fixed heaters are sequenced on
and off, the overall effect produces a continuously variable airflow
(or current) over the entire system's range.
4
above is selected (Yes),