Flowserve DDC-100 Modbus Direct-to-Host User Manual download pdf (Page 27)

48 DDC-100 Direct-to-Host Programming Guide FCD LMAIM4019-00 FCD LMAIM4019-00 DDC-100 Direct-to-Host Programming Guide 49

5.2 RS-485 Connection Direct

to the DDC-100 Field Unit

The RS-232/RS-485 converters that are sourced by Flowserve were speciﬁcally designed to comply

with the EIA RS-232 and the EIA RS-485 data transmission standards and to protect the DDC-100

Network and the Host device. The successful operation of a large number of installed systems has

demonstrated the robustness and reliability of these converters. Flowserve strongly recommends

the use of these converters for all DDC-100 applications in which the Host has RS-232 ports avail-

able. The use of these converters in most cases will simplify the installation and commissioning of

the DDC-100 Network.

If the user wishes to attach a Host device to the DDC-100 Network through other RS-232/RS-485

converters or directly from Host RS-485 ports, the following guidelines must be followed:

1) The Host ports that attach to the DDC-100 Network must adhere to the EIA RS-485 Standard.

The DDC-100 Network only uses the DATA, DATA*, and earth ground terminals. The following

additional details are provided for interfacing guidance to the Limitorque DDC-100 Network:

a) The network signal is based on +5 Volts and typical line voltage levels are

0 to 4.5 Volts.

b) Network biasing for the MX-DDC RS-485 data lines:

• terminals 15 and 16 (A1) 570 mV

• terminals 29 and 41 (A2) 280 mV

Network biasing for the UEC-3-DDC RS-485 data lines:

• D-M and D-M* (A1) 208 mV

• D-S and DS* (A2) 208 mV

Bias voltage is measured without the network attached to the ﬁeld unit RS-485 communi-

cations ports.

c) DATA is the most positive voltage and DATA* is the least positive voltage level.

d) When using RS-485 direct (without Limitorque RS-232/RS-485 converter), the user is

responsible for ensuring proper surge protection between the network and the Host device.

e) Each Host port must be resistively terminated with 120 ohms to prevent line

reﬂections.

f) The DDC-100 Field Units are certiﬁed in accordance with IEC 801-5 (EEC-EMC directive

89/336/EEC) to 1.5 kV communication lines.

2) After the Host has ﬁnished a transmission that requires a ﬁeld unit response, the Host

transceiver must be turned before the ﬁeld unit begins transmitting data back to the Host. The

ﬁeld unit can respond in 10 ms.

3) Earth ground should not be routed through sensitive electronic equipment. Connect the

network cable shield directly to an effective local, low-impedance earth ground (less than 5

ohms).

Programming

Recommendations

Programming the Host to control a DDC-100 Network of Flowserve Limitorque Field Units will

require information about the design of the network. Flowserve recommends gathering this infor-

mation before starting the program. After the program has been completed, the network should be

fully tested before commissioning. The following recommendations are provided as the result of a

number of successful installations:

1) Obtain a wiring diagram of the digital inputs and digital outputs to the controlled devices before

programming the controller.

2) Develop a tag table for the installation. This table should include the tag name, network

address, desired status indication, and command format (bit or register write).

3) If possible, test the program prior to site installation. This will provide a program veriﬁcation

time for debugging.

4) Attach a protocol analyzer to the DDC-100 Network and monitor the timing, message structure,

and message issuance to verify the Host code. This will assist in the diagnosis of proper

command issuing and sequencing of the Host control algorithm.

6.1 Monitoring Field Unit Status

Network control involves two basic functions—monitoring ﬁeld unit status and issuing control

commands. The following checklist is provided for monitoring the status of the ﬁeld units:

1) Determine the Host time-out period. Verify that the time-out period is of sufﬁcient duration to

allow a ﬁeld unit response under the worst-case conditions (greater than 200 ms).

2) Limit the number of retries to a maximum of three. This will enable the Host to continue with

the polling process without undue delays.

3) Do not allow more than one Master control of the network at any time. A Host with two serial

ports should only have one actively in control at any time.

4) The actuator ﬁeld unit digital input 0 is factory defaulted for local ESD (Emergency Shutdown).

For the MX-DDC or UEC-3-DDC, placing 24 VDC or 120 VAC (MX-DDC only) on this input will

cause the ﬁeld unit to send the actuator to the default local ESD position of close. To use this

digital input as a generic input, the local ESD setting must be set to Ignore.

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Flowserve DDC-100 Modbus Direct-to-Host User Manual Page 27

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