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This document supplies the Device-Specific Documentation for the HART-IP FlowDevice. It includes lists of the commands supported the engineering units supported, behavior of status, and interfaces to the FlowDevice
The HART-IP FlowDevice simulates a simple Coriolis flow meter. The FlowDevice measures the mass flow and the drive current required maintain the vibration of the flow tube.
As is often the case, the Flow measurement supports accurate measurement across a 10:1 dynamic range (24,000:2,400 kg/h) or (with reduced accuracy) across a 100:1 turndown. At low flow status set and the flow is coerced to 0 kg/h.
The drive current generally increases in Coriolis meters as deposits build up in the flow tube. A high drive current value sets status indication recommending maintenance be performed on the meter (clean the flow tube).
The generation of status enables publishing by exception -- A feature available in all HART 7 devices. Status is specified in the Status Information section.
The FlowDevice implements a HART 7 enabled HART-IP field device. In fact, FieldComm Group has performed standard compliance testing of the FlowDevice Application Layer to confirm conformance. The Application Layer is actually isolated and independent from HART-IP. This same Application Layer could provide a basis for HART 4-20mA or WirelessHART device
The Flow Device supports the minimal set of commands to demonstrate HART-IP capabilities including publishing ("burst-mode") runtime process and status data:
Thus the HART-IP FlowDevice demonstrates the power of publishing by exception and Smart Data Publishing.
The Flow measurement can be reported in a variety of engineering units thus demonstrating another feature of the HART Protocol.
This document provides a detailed description of the FlowDevice's features and operation. This document also identifies any tailoring of the HART Protocol by the FlowDevice (e.g., the truncation of Command 3). The details included are sufficient to enable the FlowDevice use by generic HART-IP client applications.
Device developers will find this document helpful as it provides a high-level overview. This overview could be helpful when a developer begins reviewing the HART-IP FlowDevice source code.
Users and Manufacturers that are trying to understand the possibilities offered by HART-IP may find this useful when setting up and benchmarking multiple devices. Operating multiple devices in the same network can be used to evaluate the responsiveness, latency and throughput of HART-IP networks.
PV : Primary Value
SV : Secondary Variable
TV : Tertiary Variable
QV : Quaternary Variable
The following table summarizes the device identification data/codes returned by the HART-IP FlowDevice
| Device | HART-IP FlowDevice | Device Type Code | 0xF9FD |
| Manufacturer | FieldComm Group | Manufacturer ID | 0x00F9 |
| Universal Rev. | 7 | Device Revision | 1 |
| Software Revision | 0x28 | Hardware Revision | 0x08 |
| PHY Sig Code | 6 | Device Profile | 65 / 0x41 |
The HART-IP FlowDevice demonstrates operation of a field device communicating via HART-IP. The device is a fully functioning HART 7 device and supports mandatory HART-IP commands including publishing (burst) process data and status.
The HART-IP FlowDevice is designed to operate on a Raspberry Pi 3B+ using a Waveshare Raspberry Pi High-Precision AD/DA Expansion Board. The Waveshare board includes the ADC and DAC used as the "process interface" for the field device.
Currently only the ADC on the Waveshare board is used. AD0 measures the flow rate and AD1 measures the flow tube current. In the next Device Revision will support the Flow Device Family. In that Device Revision, DA0 is planned to be used to control a batching relay.
The HART-IP FlowDevice operates on a Raspberry Pi 3B+ with a Waveshare ADC/DAC board. The Waveshare board provides the Process Interface.
The RaspBerry Pi itself has several interfaces that are possible to utilize. First, the Ethernet and WiFi interfaces support HART-IP as the primary client interface. Remote management is also possible via those channels. In addition, monitor, keyboard and mouse can be connected to the HDMI and USB interfaces respectively.
Waveshare "High-Precision AD-DA" provides the Process interface.
Flow is measured via AD0 and normally controlled via the Trim Pot (see item 8). The Jumpers (12) connect the Trim Pot to AD0. If an external Flow is to be used then the AD0-ADJ jumper should be removed. External flow voltage would be connected at Terminals (2) AD0.
All ADCs accept single-ended analog value (0-5Vdc). See ADS1256 for ADC specifications at http://www.ti.com/product/ADS1256
Likewise, Drive Current is measured via AD1 which is normally connected to the Photodetector (6). The Jumpers (12) connect the Photodetector to AD1. If an external Drive Current is to be used then the AD1-LDR jumper would be removed. External Drive Current would be connected at Terminals (2) AD1. Drive Current is reverse-acting. Full scale signal produces a low Drive Current. This is equivalent to normal operation with the Photodetector uncovered.
Future Totalizer Function The Relay is simulated using DAC0 (9) - Channel A of Texas Instruments DAC8552. Operation is binary with DAC set to zero or full scale. Jumpers (13) control whether DAC0 is connected to the LED or not. DAC0 may be connected to an external Relay to switch Flow off and on to simulate batching cycles. See DAC8552 for output specifications at http://www.ti.com/product/DAC8552.
The principal Host Interface is HART-IP. (More specifically HART-IP Version 1). This provides both publish by exception and request/response services to access the HART-IP FlowDevice. HART-IP is supported by a wide-range of client applications including data-historians, plant asset management, and many cloud-based applications.
Evaluation of the FlowDevice can be quickly undertaken using the Windows HART-IP Client. This allows low cost evaluation of HART-IP using low-cost Raspberry Pi hardware and open source software.
The Raspberry Pi 3B+ also supports Ubuntu operating system with access via ssh or with a monitor/keyboard/mouse.
There are no jumpers on the Raspberry Pi 3B+. However, the Raspberry Pi 3B+ has a number of connectors. The following are of interest:
Note: Often the system can be controlled remotely using (for example) ssh. In this case no keyboard, mouse, monitor are needed.
There are jumpers on the WaveShare PCB that control whether the onboard circuits source the "process interface" or not (item 12).
The WaveShare PCB jumpers at item 14 should be set to +5VDC.
For more information see Process Interface section above.
Returned as PV in Command 3. The following Engineering units from Common Table 2.72. are supported:
| Code | Units | Description |
|---|---|---|
| 74 | kg/min | kilograms per minute |
| 75 | kg/h | kilograms per hour |
| 81 | lb/min | pounds per minute |
| 82 | lb/h | pounds per hour |
| 84 | ton/min | short tons (i.e., 2000 lbs) per minute |
| 85 | ton/h | short tons per hour |
The FlowDevice defaults to kg/h
Limits and Accuracy Transducer limits are 0/24,000 kg/h. The Nominal flow range is 2,400/24,000 kg/h. The maximum extended flow range is 240/24,000 kg/h (with loss in accuracy below 2,400 kg/h). Below nominal flow rate Device Variable Status is set accordingly.
Note: Flow meters have about 10:1 turndown. For flows in the range 240-2400 the meter still works. - Just not so accurate.
Set Device Variable Status to “Poor Accuracy” (top 2 MSBits = 01) when low flow (
Returned as SV in Command 3
Dark means more current. Engineering units invariant as mA. Transducer limits of 0/150mA. Set "Device needs Maintenance" at current above 60mA
Normal value (e.g., 10mA) when photo resistor light is bright. 150mA when totally dark (e.g., thumb over it).
Non-PV Out of limits set when drive current > 150mA.
Returned as TV in Command 3
This is the integration of the flow into a total. This is implemented per the Totalizer Device Family Spec.
DAC0 (DAC8552 - U1) is used to as the coil driver for the relay function from the Totalizer Device Family. Full scale output from the DAC is produced when relay energized.
Totalizer shall be preset using Command 79.
Standard Device Variables 245, 249 return HART NaN
PV is fixed to "Flow" (Device Variable 0) ; SV to "Drive Current" (Device Variable 1)
“PV out of limits” set when Flow < 240
"Non-PV Out of limits" set when Drive Current >= 150mA
“Device Needs Maintenance” set when Drive Current goes hi.
"Device Variable Warning" set when flow is less than 2400 kg/h.
Command 48 Byte 0
| Bit | Status | Description |
|---|---|---|
| 0x80 | Drive current Over Range | value is >= USL |
| 0x40 | Drive current too high | flow tube is becoming plugged. device needs maintenance |
| 0x20 | Drive current Low Alarm | value is |
| 0x10 | Drive current Under Range | value is |
| 0x08 | Flow Over Range | value is >= USL |
| 0x04 | Flow High Alarm | value >= high alarm |
| 0x02 | Flow Low Alarm | Flow is less than 2400 kg/h |
| 0x01 | Flow Under Range | Flow is less than 240 kg/h |
Byte 1 thru 5 are always zero.
The HART-IP FlowDevice is HART 7 compliant and supports all the specified Universal Commands. Notes on Universal Commands Include
The HART-IP FlowDevice is HART-IP compliant and, consequently, supports burst-mode.
The following Common Practice commands are supported
Supported. Publish up to 20 updates/second per HART-IP requirements.
