OMEGA FMA-1600A Series Mass and Volumetric Flow Meters Instruction Manual
- June 17, 2024
- Omega
Table of Contents
OMEGA FMA-1600A Series Mass and Volumetric Flow Meters
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Omega MODBUS OPERATING BULLETIN
Modbus is an application layer messaging protocol that formats data for
communications among industrial devices. Omega supports both Modbus-RTU and
Modbus-TCP/IP protocols depending on the device configuration. Devices ordered
with the Modbus-RTU application layer communicate over serial RS-232 or
RS-485. Modbus data is transmitted through Omega’s default 8-pin mini-DIN
connector, a 9-pin or 15-pin D-Sub connector or an RJ45 connector.
Note
An RJ45 connecter in a Modbus-RTU device does not indicate support for
Ethernet communication or the availability of the Modbus-TCP/IP protocol in
this unit. In addition to Modbus-RTU support, your device supports standard
Omega serial commands. Please see your operating manual for a description of
the supported commands. Devices ordered with Modbus-TCP/IP support include a
dual-RJ45 connector that supports standard 10BaseT & 100BaseT Ethernet
communication. See section 3 for information on setting the device’s network
configuration.
Modbus Registers
Omega’s deployment of Modbus uses a Master/Slave structure that organizes data
into 16-bit registers. Omega supports Modbus function codes 03 “Read Holding
Registers,” 04 “Read Input Registers” and 16 “Write Multiple Registers.”
Omega devices use the Modbus PLC numbering convention such that all registers
begin at index 1.
The values seen in a Modbus Protocol Data Unit are zero-based and would be one less than those specified below. If your master controller does not follow this convention, you may need to decrease register addresses by one. All 32-bit values are handled in consecutive Modbus registers in big-endian format. This means bits 31:16 are in the lower numbered Modbus register and bits 15:0 are in the higher register. All floating-point values are IEEE 32-bit floats.
| Parameter | Access | Register Number | Description |
|---|---|---|---|
| Command ID | RW | 1000 | See Section 1.1 |
| Command Argument | RW | 1001 | |
| Setpoint | W | 1010-1 | See Section 1.2 |
| Mixture Gas 1 Index | RW | 1050 | See Section 1.3 |
| Mixture Gas 1 Pct | RW | 1051 | |
| Mixture Gas 2 Index | RW | 1052 | |
| Mixture Gas 2 Pct | RW | 1053 | |
| Mixture Gas 3 Index | RW | 1054 | |
| Mixture Gas 3 Pct | RW | 1055 | |
| Mixture Gas 4 Index | RW | 1056 | |
| Mixture Gas 4 Pct | RW | 1057 | |
| Mixture Gas 5 Index | RW | 1058 | |
| Mixture Gas 5 Pct | RW | 1059 | |
| Gas Number | R | 1200 | See your Omega operating manual for a list of gas numbers |
| Device Status | R | 1201-02 | See Section 1.4 |
| Device Statistic 1 Value | R | 1203-04 | |
| Device Statistic 2 Value | R | 1205-06 | |
| Device Statistic 3 Value | R | 1207-08 | |
| Device Statistic 20 Value | R | 1241-42 |
Device Commands
Commands can be issued to the Omega device using Modbus register 1000.
Commands are described in the table below. Some commands require a parameter
to be passed in Command Argument register 1001 using the “Write Multiple
Registers” Modbus function code. A write to only the Command ID register 1000
will be interpreted as having a value of 0 in the Command Argument. Commands
take effect after a Modbus write command. Reads of the ID register 1000 will
return the last executed command. Reads of the argument register 1001 will
return the status of the last executed command (see next page).
| Command ID | Action | Argument |
|---|---|---|
| 1 | Change gas number | Gas Table Index |
| 2 | Mix gas | Gas mixture index (236-255) or 0 to use next available |
| 3 | Delete gas mixture | Gas mixture index |
| 4 | Tare | 0 = Pressure |
1 = Abs Pressure 2 = Volume
5| Totalizer reset| None
6| Valve setting
Exhaust is only supported on dual-valve devices
| 0 = Cancel
1 = Hold close 2 = Hold current 3 = Exhaust
7| Display lock
Only supported on devices with a display.
| 0 = Unlock
1 = Lock
8| Change P in PID Loop| 0-65535
9| Change D in PID Loop| 0-65535
10| Change I in PID Loop| 0-65535
11| Change control loop variable.| 0 – Mass Flow
1 – Volumetric Flow
2 – Diff Pressure
3 – Absolute Pressure 4 – Gauge Pressure
12| Save current set-point as power-up value.| None
13| Change control loop algorithm.| 1 – PD
2 – PDDI
14| Read PID value| 0 – PID P
1 – PID D
2 – PID I
32767| Change Modbus Slave ID – Modbus/RTU only.| New ID 1-247
Setpoint
The device setpoint should be sent as a 32-bit IEEE floating point value. Setpoint values must be sent together in a Write Multiple Registers command. Any writes to only one-half of the setpoint value will cause an error. Setpoint is ignored on devices without a controller.
| Status | Description |
|---|---|
| 0 | Success |
| 236-255 | Gas mix index that was created or updated (Mix gas command only) |
| 0x8001 | Invalid command ID |
| 0x8002 | Invalid setting |
| 0x8003 | Requested feature is unsupported |
| 0x8004 | Invalid gas mix index |
| 0x8005 | Invalid gas mix constituent |
| 0x8006 | Invalid gas mix percentage |
Gas Mixing
Gas mixing can be performed with 2-5 gases using the mix registers 1050-1059.
The mix is a two-step process. First, the desired constituent gas indexes and
percentages must be written to the mixed registers followed by a write of the
Mix Gas command (ID 2) into the command register 1000 (with the command
argument being optional). Gas mix percentages are interpreted as integer
hundredths of a per cent and the total percentage must sum to 100%. For
example, to specify a mix of 50%, a value of 5000 should be written into the
gas percentage register. The mix will be performed with the first N gases that
have a nonzero percentage. As an example, if you wish to mix 3 gases, you
would write the index and percentage for those gases into registers 1050-1055
and write a value of zero into 1057-1059.
If the command argument passed to the mix command is 0 or is omitted, a new gas mix index will be allocated in the next empty gas mix index starting at 255 and working down to 236. If no user mix indices are unused, the command will not be completed and an error will be returned in the command argument register. If the command argument passed is between 236 and 255, the mixture with the specified index will be either created or updated to the new composition. If the specified index is not valid (the command argument is neither 0 nor 236-255), an error will be returned.
Upon completion of mixing, the command argument register will be updated with
the mix result. If the mix is valid, the index of the mixed gas will be
returned. If one of the requested mix gas constituents does not exist or the
percentage does not add to 100%, an error value will be returned and the mix
will not be created.
Note : Gas mixing is only available over the Modbus serial interface and
cannot be performed from the front panel display. All gas mixtures are
accessible via Gas Select on the front panel, but mixtures may not be created
or deleted via the front panel.
Device Status
This register specifies status conditions in the device. The value in
parenthesis is the front-panel display of the corresponding condition.
| Bit | Description |
|---|---|
| 0 | Temperature Overflow (TOV) |
| 1 | Temperature Underflow (TOV) |
| 2 | Volumetric Overflow (VOV) |
| 3 | Volumetric Underflow (VOV) |
| 4 | Mass Overflow (MOV) |
| 5 | Mass Underflow (MOV) |
| 6 | Pressure Overflow (POV) |
| 7 | Totalizer Overflow (OVR) |
| 8 | PID Loop in Hold (HLD) |
| 9 | ADC Error (ADC) |
| 10 | PID Exhaust (EXH) |
| 11 | Over pressure limit (OPL) |
| 12 | Flow overflow during totalize (TMF) |
| 13 | Measurement was aborted |
Device Statistics
Your Omega device can output 20 different configurable data statistics. The
default statistics for each device type are specified in the sections below.
For Modbus-RTU devices, the actual statistic and unit output on your device
can be determined by issuing the Omega data frame query command (??D). For
Modbus-TCP/IP, the available statistics are viewable from the device’s
embedded web server. To access, point your web browser to the device’s IP
address and select the Data I/O tab. If you wish to customize the output of
your device please speak to an Omega applications engineer.
Unless specified below, all output values are in 32-bit IEEE floating point. If an unused device statistic slot is read on Modbus-RTU, the value 0xFFFFFFFF will be returned. On Mobus-TCP/IP devices unused slots will return an invalid register address error. The value returned for a pressure reading can be absolute pressure, gauge pressure or differential pressure depending on your device’s configuration.
Mass Flow Controller
Mass Total is only available on units with the Totalizer option.
| Register Number | Statistic |
|---|---|
| 1203-04 | Pressure |
| 1205-06 | Flow Temperature |
| 1207-08 | Volumetric Flow |
| 1209-10 | Mass Flow |
| 1211-12 | Mass Flow Setpoint |
| 1213-14 | Mass Total* |
Mass Flow Meter
Mass Total is only available on units with the Totalizer option.
| Register Number | Statistic |
|---|---|
| 1203-04 | Pressure |
| 1205-06 | Flow Temperature |
| 1207-08 | Volumetric Flow |
| 1209-10 | Mass Flow |
| 1211-12 | Mass Total* |
Pressure Gauge
| Register Number | Statistic |
|---|---|
| 1203-04 | Pressure |
Pressure Controller
| Register Number | Statistic |
|---|---|
| 1203-04 | Pressure |
| 1205-06 | Pressure Setpoint |
Legacy Registers
For backward compatibility, the following legacy registers are supported on the Modbus-RTU protocol. These registers are not available on Modbus-TCP/IP devices. Unlisted registers are not configurable via Modbus. Please consult Omega for assistance if additional configuration is required.
User-Accessible Configuration Registers
For new deployments, Omega recommends using the Device Command Registers above
to set these values.
| Parameter | Access | Register Number | Description |
|---|---|---|---|
| PID control loop P | RW | 21 | 16-bit integer |
| PID control loop D | RW | 22 | 16-bit integer |
| PID control loop I | RW | 23 | 16-bit integer |
| Setpoint | RW | 24 | 0-65535 with 64000 equal to 100% of full scale range. |
| Gas Selection | RW | 46 | 16-bit integer |
| Modbus device ID | RW | 65 | 1-247 |
Device Data Registers
Omega uses read-only Modbus registers 2,041-2,059 to hold the values of the
instrument data as follows:
| Query | Register Number | Data Type |
|---|---|---|
| Pressure | 2041-2042 | 32-bit float* |
| Temperature | 2043-2044 | 32-bit float* |
| Volumetric Flow Rate | 2045-2046 | 32-bit float* |
| Mass Flow Rate | 2047-2048 | 32-bit float* |
| Setpoint | 2049-2050 | 32-bit float* |
| Totalized Mass Flow | 2051-2052 | 32-bit float* |
| Modbus Device ID | 2053 | 16-bit integer |
| Gas Number | 2054 | 16-bit integer |
| Vol. Flow Overage (VOV) | 2055 | 0=ok, 1=error exists |
| Mass Flow Overage (MOV) | 2056 | 0=ok, 1=error exists |
| Pressure Overage (POV) | 2057 | 0=ok, 1=error exists |
| Temp. Overage (TOV) | 2058 | 0=ok, 1=error exists |
| Totalizer Rollover (OVR) | 2059 | 0=ok, 1=error exists |
Modbus-TCP/IP Configuration
Omega Modbus-TCP/IP devices have two 10/100Mbps Ethernet ports with an embedded switch. Either port can be used to communicate with the device. In addition, the embedded switch supports packet forwarding allowing daisy- chaining devices in a linear or ring topology.
Address Configuration
The out-of-the-box configuration of your device is to use DHCP to obtain an IP
address. There is an embedded web server in the device which supports
assigning a static IP address to the device. To do so, you must first assign
an address using DHCP. The following shows an example of configuring the
address using Microsoft Windows: First, assign a static IP to an unused
network interface:
Second, configure a DHCP server to give a known IP address to your device on the static network. This example uses the open-source Tftpd64 tool (http://tftpd32.jounin.net): After connecting your Omega device directly to the static port and supplying power to the device, you should see an address allocated to the device by the DHCP server: The network configuration can then be changed using the device’s embedded web server. Navigate to the Network Config tab, uncheck the “Use DHCP” box, and enter the desired static IP address into the form.
References
- Omega Engineering | Sensing, Monitoring and Control Solutions
- Global Presence | Omega Engineering
- TFTPD64 : an opensource IPv6 ready TFTP server/service for windows : TFTP server