Overview
Over the last four years a complete infrastructure useable for automatic meter reading fluid flow and energy measurements has been developed. This system includes raw sensors and front end electronics to measure fluild flow rates and temperatures, and capture pulse counts and rates. It also includes a local area ISO certified ANSI standard network and packet transport mechanisms both wired and wireless onto the internet. Over a million dollars in engineering has been invested.
Functional electronics, and ready firmware for all the facets of this system have been developed. The electronics is the current state of the art using an advanced in-system programmable, mixed-signal System-on-Chip processor. There are very few external parts for any system component, and each component can run on extremely low power required.
Detailed Technical Description
A small circuit board design has been completed that contains a power supply, and sensor front ends. This board makes measurements of pulse trains, both count and rate, from near DC to 22 kHz. It includes thermistor and RTD front ends used to measure temperature differentials need for heating and cooling power meters. It has a pulse train generator that can be used to send out a pulse rate proportional to any of the sensor inputs. It has RS-485 communications used as the electrical layer of the BACnet (Building Automation and Control) MS/TP (Master Slave/Token Passing) protocol and data encapsulation. The firmware is specifically tailored to meter reading, supporting objects defined by the standards committee for this exact industry.
- Firmware is in ANSI standard C with assembler where required.
- Programming is written according to structured and variable naming standard guidelines.
- System design is modularized.
The algorithms used for thermistor normalizations and engergy/enthrapy calculations exceed industry requirements.
One form factor for the meter electronics is a potted assembly as shown here.
Also developed is a version with a 180x64 pixel graphic display with relevant
fixed ICONS. This display though fully graphic is low cost. It uses self
contained COG, (Chip on Glass), technology to simplify construction and minimize
part count. It has 8 K of internal RAM a driver chip, and all the LCD driver
power supplies on the glass. It takes micro-amps to run.
Internet Gateway
Also developed is a gateway/router that communicates with a BACnet MS/TP RS- 485 network. It is a small single processor, low cost board that translates protocols between the 485 protocols and Motorola's CLP interface on the ReFLEX wireless telemetry network. ReFLEX radios and telemetry service charges are very cost efficient. Each radio puts the connected equipment directly onto the internet with an always live two way connection using binary and communication direct to fixed IP addresses.
The gateway board can tie to up to 64 devices on a local twisted pair wired network. All connected devices can be all in the same area or up to 4000 feet away. This offers the option between using multiple radio gateways, and interconnecting multiple meters with extended wiring.
Conclusion
This system is applicable to many industrial, agricultural, and residential metering and instrumentation applications. Each meter board can run on only micro-amps of power allowing use where line power is not available. For agricultural applications the sensor nodes can be made to control values and send back weather and system statuses. The ReFLEX radios can be exchanged for other digital wireless devices, cellular, satellite, direct point to point and point to multi-point.
Central to the design is the industry standard network and data encoding. Using BACnet other devices from other manufactures can share the same network and interact with this sensor device.