Instruction manual

18
3–13 Manual Control
Operation
To enable manual control, the LOCK parameter should be set
to NONE, then press for 6.2 seconds;
(hand control) will appear on the display. Press for 5 sec-
o
nds, then the MAN indicator will begin to flash and the
lower display will show . The controller is now in
manual control mode. indicates output control vari-
able for output 1, and indicates control variable for
output 2. Now you can use the up and down keys to adjust
the percentage values for the heating or cooling output.
The controller performs open loop control as long as it stays
in manual control mode.
Exit Manual Control
Pressing the key will cause the controller to revert to its
normal display mode.
3–14 Data Communication
The controllers support RTU mode of Modbus protocol for
data communication. Other protocols are not available for
this series.
Two types of interface are available for data communication.
These are RS-485 and RS-232 interface. Since RS-485 uses
a differential architecture to drive and sense signal instead of
a single-ended architecture like the one used for RS-232, RS-
485 is less sensitive to noise and suitable for communication
over a longer distance. RS-485 can communicate without
error over a 1km distance while RS-232 is not recommended
for a distance of over 20 meters.
Using a PC for data communication is the most economical
method. The signal is transmitted and received through the
PC communication port (generally RS-232). Since a standard
PC can't support an RS-485 port, a network adapter (such as
TEC 99001) has to be used to convert RS-485 to RS-232 for
a PC if RS-485 is required for data communication. Up to
247 RS-485 units can be connected to one RS-232 port;
therefore a PC with four comm ports can communicate with
988 units.
Setup
Enter the setup menu. Select RTU for COMM. Set individual
addresses for any units that are connected to the same port.
Set the baud rate (BAUD), data bit (DATA), parity bit (PARI)
and stop bit (STOP) so that these values are accordant with
PC setup conditions.
If you use a conventional 9-pin RS-232 cable instead of
TEC99014, the cable should be modified for proper opera-
tion of RS-232 communication according to section 2-9.
Refer to chapter 7 for a complete technical description of the
Modbus Communications Protocol.
R
3–15 Process Variable (PV)
Retransmission
The controller can output (retransmit) the process value via
its retransmission terminals RE+ and RE- provided that the
retransmission option is ordered. A correct signal type should
be selected for COMM parameter to meet the retransmission
o
ption installed. RELO and REHI are set to specify the low
scale and high scale values of retransmission.