Ametek Land 4750-PM, User Manual

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4 - 9 User Guide
Particulate Measurement System 4750-PM
4.5.4 Bus Termination Switch
Fig. 4-6 Bus Termination Switch
Refer to see Fig. 3-3 on page 3-3 for the location of the Bus Termination
Switch (Item 5)
If the sensor is in the middle of the network, set the bus termination switch
to U (un-terminated)
If the sensor is at the end of the network and for single-channel systems, the
switch must be set to T (terminated).
4.5.5 Communications Settings (SW7)
Setting the Network Address
Each sensor must have a unique address on the network (for ON = switch
position is to the LEFT). The Modbus address is set by means of the dip
switch (see item 11, Fig. 4-2 for its location) using a suitable implement
(such as a small flat-blade screwdriver).
Only switches 1 through 5 are used to set valid addresses (from 1 to 32).
The address switch uses binary coding to calculate the address.
Example: to set sensor address number 5: set both switch 1 (binary 1) and
switch 3 (binary 4) to ON = LEFT (resulting in 4 + 1 = 5).
MODBUS Communications Settings
Both Modbus communications protocols, ASCII and RTU, are available and
can be set via the dip switch (see item 11, Fig. 4-2 for its location). Use
switch positions 6 through 8 to define the communications protocol settings.
Note that the baud rate is set to default value. Use switches 6 and 7 to
define the baud rate; currently both switches are set to OFF (RIGHT) for the
default baud rate.
RTU is a faster communications protocol than the standard ASCII protocol.
For RTU mode set switch 8 to OFF (RIGHT), meaning parity is set to ‘none’ or
to ON (LEFT) for ASCII, meaning parity is set to ‘odd’.
The settings are as follows:
Setting Value Setting Value
Baud rate 19200 (default) Stop bits 1
Parity None (Modbus RTU)
Odd (Modbus ASCII)
Data bits
(Comms mode)
8 (Modbus RTU) or
7 (Modbus ASCII)