Reference, Installation, and Operations Manual

Section 2: Product overview

3-9000-743 Rev S

June 2013

 

 

 

2.6Communications

The Daniel Mark III Ultrasonic Gas Flow Meter provides two standard and one optional RS-232/RS-485 serial communication ports (referred to respectively as Port A, Port B, and Port

C)and an optional Ethernet port (Eth1). Port A and B are expected to be used for (general) communication with flow computers and RTUs. Port C (included on the Option Board and the Series 100 Plus Option Board) can be used for general communication (such as with a flow computer or RTU) or for optional communication as a Modbus master with a Daniel Gas Chromatograph (GC). With the Series 100 Plus Option Board installed, you can establish communications with other devices via a Field Communicator (375) or AMS™ Suite). The Ethernet port is expected to be used for diagnostic purposes. See Section 5.8 for software configuration of communications protocols.

Port A is the preferred port for connection to a flow computer or RTU. If two flow computers are to be connected to the meter, then Port B should be used to connect to the second flow computer. If a computer running the Daniel MeterLink program is to be connected to a meter and the optional Ethernet port is enabled, it is the preferred port for the connection. If the Ethernet connection is not feasible, then Daniel MeterLink should be connected to the meter using Port B in full duplex configuration.

Daniel MeterLink will not communicate with a Mark III meter over a half-duplex serial connection.

Both Ports A and B are individually hardware-selectable for RS-232/RS-485 Full Duplex/RS-485 Half Duplex operation. Port A supports RS-232 RTS/CTS handshaking with software-configurable RTS on and off delay times. When handshaking is enabled, Port A drives the RTS output low and expects the CTS input to be active low. Both Ports A and B support individually software -configurable transmit delay times.

Port C (provided by the Option Board and the Series 100 Plus Option Board) is individually hardware -selectable for RS-232/RS-485 Half Duplex operation. Port C supports a software-configurable transmit delay time.

Ports A, B, and C support ASCII and RTU Modbus protocols (as detailed in Table 2-11) which are automatically detected on a per-port basis.

Table 2-11 Supported Modbus Protocols
Modbus ProtocolNumber of Start BitsNumber of Data BitsParity TypeNumber of Stop Bits

 

 

 

 

 

ASCII

1

7

odd or even

1

 

 

 

 

 

RTU

1

8

none

1

 

 

 

 

 

Modbus addresses are software configurable (from 1 to 247) on a per-port basis. Ports A and B operate only as Modbus slaves. Port C can operate as either a Modbus slave (for general communication) or a Modbus master (for GC communication).

Baud rates are software selectable on a per-port basis from the following:•ASCII Modbus: 1200, 2400, 9600, 19200, 38400, 57600, 115000 bps•RTU Modbus: 1200, 2400, 9600, 19200, 38400 bps

Communications

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