Instruction manual

Introduction
025-9209 3
A MODBUS SCADA system with a Model 1700 controller is shown in Figure 2.
In a MODBUS system, the PC can communicate with up to 150 Model 1708 or Model 1716
RTUs over radio or wireline through a single Model 1700 controller. A system can be
expanded beyond 150 RTUs by adding additional controllers and using additional serial ports
on the PC. The total number of RTUs in a system is limited only by the number of serial
ports available on the PC, and by the MODBUS slave address limit of 247.
Modbus PLC
- or -
PC with Modbus
SCADA Program
M1708/
M1716
M1708/
M1716
M1708/
M1716
RF
RF
RF
RS232
MODBUS Protocol
M1708/
M1716
RF - Store & Forward
Note: all RF connections could be replaced with leased lines
M1700
with
MODBUS
option
M1708/1716
with
MODBUS
option
RS232
MODBUS
Protocol
Figure 2. Generalized MODBUS System
CONNECTIONS
Main Power
Flow Detector
Door Open
High Water
High Temperature
Panic Button
Model 1716
Remote Terminal Unit
Digital #1
Inputs
•
•
•
#16
A
nalog #1
Inputs •
•
•
#8
Digital Outputs
#16 • • • #1
Radio Connections
Battery Level
Tank Level
Pump Control On/Off
A
larm On/Off
Panic Acknowledge On/Off
Back Up Power On/Off
Figure 3. Model 1716 RTU Standard Connections for a Pump Site
A standard application of monitoring and controlling a remote pump site could be
accomplished by using output #1 to control the pumps on/off switch and by connecting input
#1 to a flow meter to determine if the pump is pumping. If the control relay on the RTU is
damaged, the pipe is blocked, or a short or open circuit to the pump control has occurred,
then the RTU will report that no liquid is flowing.