Peaktronics DHC-100 User Manual

22
Registers 1, 19, and 20 with function code $03 or $06, the
request is processed directly by the OCM-101, and response
times are shown below.
Response Time (Registers 1, 19, and 20)
RTU mode t
RESP
min t
RESP
max
(baud) (usec) (usec)
9600 4,010 5,166
19200 2,005 2,588
57600 668 869
115200 334 440
ASCII mode t
RESP
min t
RESP
max
(baud) (usec) (usec)
9600 208 325
19200 104 166
57600 35 62
115200 18 36
When using the PACS
®
function ($41) or accessing
registers other than 1, 19, or 20 with function code $03 or
$06, response times are more dependent on the DHC
controller since it must perform many other tasks. The
response times are given below.
Response Time - (except Registers 1, 19, and 20)
RTU mode t
RESP
min
(baud) (usec)
9600 4,010
19200 2,005
57600 1,500
115200 1,500
ASCII mode t
RESP
min
(baud) (usec)
All 1,500
t
RESP
max (RTU or ASCII, all baud rates):
13 msec (normally)
50 msec (once every 15 minutes)
The DHC controller saves information in non-volatile
memory once every 15 minutes. Pushing the Mode
button on the DHC control panel also triggers a save to
non-volatile memory. If the DHC receives an ADU at
that moment, t
RESP
max could be 50 msec. Otherwise
t
RESP
max is 13 msec.
USING A DIGITAL COMMAND TYPE
To control the DHC controller with a command
signal from the bus instead of from an analog input, the
DHC must
first be configured for a Digital command type
using the COMMAND TYPE mode; the command input
type cannot
be selected via the bus. When configured for a
Digital command type, the DHC ignores any analog
command signal that may be connected, and the Analog
Command Input parameter will read zero.
On power up, the DHC controller will detect a loss
of command until it receives the appropriate bus commands
for controlling the actuator. Bit 0 of the Alarm Flags
parameter will be set to "1", and the DHC controller will
move the valve to the default position (open, closed, or last
position) as set by the LOSS OF COMMAND mode from
the DHC control panel. If desired, the default position can
be changed via the bus using bits 4 and 5 of the PACS
®
Control Register parameter.
To provide the command signal value to the DHC,
the Modbus master device writes the desired position value
(0 to 10000, representing 0% to 100% open) to the PACS
®
Command Input parameter. However, the DHC controller
will not act on the command value until the PACS
®
Timeout Setting parameter is set to a non-zero value; this
parameter is cleared to $00 when the DHC powers up.
Upon setting the timeout value (1 to 255, representing 0.5
seconds to 127.5 seconds), the DHC immediately clears the
loss of command alarm and begins moving the valve to the
desired command value.
Since the command input value is also cleared to
$0000 on power up, it makes sense to write the command
input value before setting the timeout value. Note, writing
the PACS
®
Command Input parameter with function code
$06 automatically sets the timeout value. Once the timeout
value is set, it is not necessary to rewrite it unless the DHC
controller loses power. So the command input value can be
updated at regular intervals without having to rewrite the
timeout value.
Momentary power drop outs are common in
industrial applications and could very likely occur between
updates of the command value. This means that the bus
master will need to know that power was lost, so that it can
rewrite the timeout value if power was lost. To monitor for
a power drop out, bit 7 of the PACS
®
Control Register
parameter (00ED SING) is set to "1" via the bus using
PACS
®
function ($41). Since a power drop out will cause
bit 7 to be cleared to "0", the bus master can detect that a
power loss occurred by monitoring bit 7 at whatever
interval is suitable for the application.
Based on the previous discussion, a logical
initialization sequence for the DHC controller can be
derived. Consider the following example sequence.
DHC Controller initialization sequence
PACS
®
Command (ORS#ED,#80) 6A 00 ED 80
This sets bit 7 of the PACS
®
Control Register
parameter to "1" to allow monitoring for a power
loss. If the DHC does not respond after 200msec,
or returns an error response, continue with the next

Peaktronics DHC-100 Specifications

General

Brand	Peaktronics
Model	DHC-100
Category	Controller
Language	English