Dwyer MS2-M - Manual (Page 2)

electrical Wiring
Figure 1 shows how to connect the MS2 in a network containing a common power
supply. Use a cable containing two twisted pairs. One pair is to be used for B(+)
and A(-). The other pair is to be used for power and common. This configuration is
not suitable for AC supplies. Use a DC supply only. Care should be taken that there
are not too many devices powered from the same supply as voltage drops will
occur in the wiring. If you have many devices, or have long cable runs, the local
supply configuration may be a better choice.
Figure 2 shows how to connect the MS2 in a network containing individual local
supplies. Use a cable containing a twisted pair and a single conductor. The pair is
to be used for B(+) and A(-). The single conductor is to be used for common. Both
AC and DC supplies are suitable for this configuration.
In either configuration you must use shielded cable. The MS2 has a shield terminal
for a convenient location to make connections. It is not electrically connected to the
MS2. Connect the shield to earth ground at one location only to prevent ground
loops.
All devices in the network should be daisy chained. Star connections and T
connections are not permitted.
The B(+) and A(-) lines must be terminated at both ends with a 120 ohm resistor.
If the MS2 is an end device it has an on-board resistor that may be used. See DIP
SWITCH SETTINGS to enable it.
The network must be biased properly. If needed, there are bias resistors on-board
the MS2. No more than two sets of bias resistors should be enabled in the network.
See DIP SWITCH SETTINGS to enable them.
Dip Switch Configurations
Use the left DIP Switch SW1 to configure the Modbus ® Communication Protocol
address of the device. The LCD will show the address when the transmitter is
powered on. Valid addresses range from 1 to 247. By default, the device is shipped
with the address 127 (as shown in Figure 3). A valid and unused address should
be set before connecting to an existing network. However, the address can be
changed while the device is operational. If the address is changed, the device will
stop responding to the currently configured address immediately. The device waits
15 seconds after the last switch change before applying the new address. The
device will not function properly if an invalid address is set. The red LED will
periodically blink once indicating an invalid address. The LCD will display “A Err”
when the transmitter is powered on if the address is invalid. See Appendix I for
setting the Modbus
® Communication Protocol address of the device.
Use the right DIP Switch SW2 to configure other hardware and software options.
Table 1: DIP Switch SW2 functions
Table 2: Display Units Selection
Wiring should comply with Electrical Characteristics of
Generators and Receivers for Use in Balanced Digital Multipoint
Systems, TIA/EIA-485-A-1998, Telecommunications Industry Association, 1998.
NOTICe
Wiring should comply with Modbus ® Communication Protocol
over Serial Line Specification and Implementation Guide V1.02,
Modbus Organization, Inc., 2006
NOTICe
Communications wiring must be in a daisy-chain fashion. Star
connections are not permitted. NOTICe
Cable shield must be connected to earth ground at one location
only. NOTICe
COMMON POWER SUPPLY
B(+) A(-) PWR COM SHIELD
TO NEXT
DEVICE
TO PREVIOUS
DEVICE
B(+)
A(-)
PWR
COM
B(+)
A(-)
PWR
COM
figure 1
B(+) A(-) PWR COM SHIELD
POWER
SUPPLY
LOCAL POWER SUPPLY
+ -
B(+)
A(-)
COM
B(+)
A(-)
COM
figure 2
ON
1 2 3 4 5 6 7 8
figure 3
figure 4
Switch
1-2 – Display Units
Selection
(See Table 2)
3-4 – Reserved
5 – Full Intelligent Serial
Configuration
6 – B(+) Network Resistor
7 – A(-) Network Resistor
8 – Terminating Resistor
On
Enabled
511Ω Pull-up to 5V
511Ω Pull-down to GND
120Ω between A(-) & B(+)
Off
Disabled
Pull-up not connected
Pull-down not connected
Open
When using the on-board buttons, there is a 5 second delay
from the time the zero or span calibration button is released until
the time that the change in calibration takes place. This delay is used to prevent
stress related offsets on the lower ranges.
NOTICe
The security level that is set in the Programming Menu Section
of the manual will determine which calibrations, if any, may be
adjusted by the user through the on-board buttons, but the calibration can be
changed at any time through the communications.
NOTICe
Switch 1
OFF
ON
OFF
ON Switch 2
OFF
OFF
ON
ON Unit
Inches of Water Column (in WC)
Pascal (Pa)
Millimeters of Water Column (mm WC)
Kilo-Pascal (kPa)