Technical overview.

Both probeLink and smartBase modules are used in reading and transmitting field data from sensors supplied by others. They can be used independently or together.

The probeLink controller has a three wire interface to the outside world which can operate either as a standard SDI-12 master controller or as a three wire RS232 slave device using Modbus ASCII protocol. When not using SDI-12 to communicate with sensors, the unit automatically looks for Modbus ASCII commands on the line.

A future development of the probeLink will be allowing it to operate as an SDI-12 slave device. This will allow a network of SDI-12 sensors to be accessed via the final probeLink unit acting as a slave.

probeLink is equipped with an inbuilt radio transceiver, currently this is either a 433MHZ or 151MHZ radio which uses the license free radio bands available in most countries. Detailed descriptions given later will cover the use in Australia, if the units are being deployed elsewhere then it will be important to order the correct radio for the destination.

The probeLink controller can be configured through the radio transceiver using a modem based on an equivalent radio module.

smartBase modules basically provide the connections to easily install a probeLink unit in the field, although the user may decide on other arrangements. There are two variants of it available at the moment.

Both current versions of the smartBase contain a four wire terminal block used to connect a solar panel and battery. There is an onboard solar regulator which will provide charge to the battery, it has certain smarts to detect battery fully charged and control the charge rate.

Another four 3 -wire connectors are also placed along the edge of the smartBase. These are all wired to the SDI-12 electrical specification. There is a slight difference in the first connector and it is meant to connect a probeLink device.

There is also a standard 9 pin RS232 connector for communication with an attached probeLink unit.
smartBase2 is provided with a microprocessor which can be configured to read other sensors beside the standard SDI-12 ones. Details are given later

In the future there will be other smartBase modules developed to perform different tasks such as controlling pumps and solenoids.



Design Features of the probeLink Controller.

The probeLink device has been designed to specifically read and transmit SDI-12 sensors. The design attempted to address the following issues:

1. Cost. Final cost was a big factor, users were demanding less expensive products to install in their systems. This meant that some of the features, like reading RS485 sensors, which were in previous versions of the IPC devices, were removed. Other types of sensors can be accommodated, if required, through the use of the smartBase range of modules.

2. Stand Alone Device. The controller should be a standalone device which could be used to create a network of sensors which were either polled from a central location or which were automatically transmitted to a final receiver and read by a data recorder or a gateway to the internet.

3. Enclosure and Cabling. It was decided to use the current probeLink enclosure because it was small and appropriate for the 433 and 151 MHZ monopole antennas with which it would be used. This meant there was only space for one cable to exit the enclosure and we chose to make this the standard 3 wire SDI-12 connection. A compact 3 way terminal block inside the enclosure connects to the standard SDI-12 power, data and ground connections.

4. SDI-12 Connection. This connection is primarily used to connect the probeLink with up to 3 SDI-12 sensors. The setup and configuration of the probeLink can be done via radio. The radio setup is a good idea and certainly allows the user more flexibility with accessing targets from a central location. However there is also a need to connect a PC locally to the probeLink. It was decided to do this over the SDI-12 connection. This meant that the connection had to be shared between communicating with a PC and reading the sensors

5. Connecting an RS232 Device. The probeLink shares the use of the 3 wire SDI-12 connection by implementing a half duplex RS232 link using Modbus ASCII protocol. In order to allow this to happen it was necessary to implement a signaling system which would prevent the PC or other device using the RS232 connection from using the bus when it was being used by the probeLink to scan sensors. This was achieved by an adaption of the XON/XOFF signaling sometimes used in serial communications. These are short strings sent regularly containing embedded XON/XOFF characters which the PC looks for before making contact. This is why, when you select the half duplex cable connection mode to the probeLink, the iCommunicator program generally puts up a flag "Waiting for Clearance". It does not need this clearance generally on the radio link, that is handled in other ways. The frequency of this permission signal varies at different times.

6. Speed of RS232 Connection. It is not necessary to disconnect the sensors in order to use the RS232 communications to probeLink. However the sensors have inbuilt impedance and capacitance which is suited for 1200 baud SDI-12 communication. This means that if sensors are connected, particularly if there are several, then it is wise to use 1200 baud communications with the PC. Indeed the probeLink defaults to this speed although iCommunicator can change this. Because there is such a small amount of traffic on the interface the lower speed is not an issue.

7. Variation in the sending of the permission flags. When the probeLink is first powered on, it spends the first 10 seconds looking to see if the firmware upgrade program is going to run. No other communication can take place during that time. For the next 60 seconds probeLink will not try to access the sensors, this leaves the link at the full use of the PC. During this time the XON strings are sent every 4 seconds. If you want to ensure quick connection then power down/up the probeLink, wait 10 seconds and then communicate with it. As long as the probeLink is receiving valid requests from the PC it will not try accessing the sensors. A timeout period of 12 seconds applies. If the PC delays for more than 12 seconds then the probeLink may use the channel for sensor activity. After the initial 60 seconds, probeLink will start scanning sensors at the configured scan period. Before it does this it sends an XOFF string to the PC and then an XON signal when the scan is finished. The XON signals are then sent every 10 seconds if the probe is not being accessed. The iCommunicator program will wait for 15 seconds for permission before giving up. There are options to disable this regular sending of the XON string where power saving is an issue. If that method is used then the probeLink must be powered down/up so that the PC can communicate in the first 60 second window.


8. Choice between Radio and Cable Setup. There are some setup functions which are best handled over the dedicated serial cable. In particular setting the address of the probeLink node. If the radio is used then all devices within the radio range will be altered, which is undesirable. iCommunicator also has the facility to reset or reset the target or reset to default values. Obviously this is not something which should be sent to a network over the radio. Otherwise setup using a radio modem is an ideal way to configure the network and this was at the forefront of the design.


Using probeLink.

The probeLink controller is equipped with a built on radio and an SDI-12 connection. It is meant to collect data from up to 3 SDI-12 devices with addresses 0 through 2 and either send the data at predetermined intervals over the radio or wait to be polled over the radio from a central location.

The configuration of the unit is partly done by allowing probeLink to automatically detect the SDI-12 sensors which are attached. While this uses generic SDI-12 commands and most new sensors will be detected correctly, the iCommunicator program has been structured to work best with sensors which have already been tested and approved by NRIE. The profile for these sensors is built into the probeLink and it knows how to process them automatically. NRIE will normally provide the service of connecting new sensors and building their profile into the firmware if a sample sensor is provided.

probeLink operates in two modes over the radio network, polled and asynchronous transmission.

In the polled mode, data is retrieved from the network using a radio modem at some central location. This means the central controller has to be able to send Modbus ASCII commands to the network and process the data it receives. Currently there is no repeater function built into the network for the polled mode. This is planned as an upgrade in the near future.

In the asynchronous transmission mode the probeLink will take a reading at determined intervals and send it to another probeLink device or to a controller listening for Modbus ASCII register transmissions. The receiving probeLink packs the information it receives into a table if it is configured as a final receiver or repeats it to the next probeLink if it is configured as a repeater. The asynchronous mode suits the slow changing data which these units are normally used with.



Using the smartBase Modules.

It is not necessary to pair the smartBase and probeLink units, probeLink is meant to operate as a self-contained unit however the smartBase provides several advantages;

1. smartBase Convenience. The design grew out of many years of installing and operating field devices. It is often necessary to isolate sensors or connect new ones without disturbing existing wiring. smartBase provides a separate connector for each sensor and the probeLink controller. This makes it easy to unplug individual sensors. It also allows the wiring to be logical and intuitive.

2. Inbuilt Solar Regulator. The basic smartBase module contains a solar regulator which can be used with up to 10W solar panels and 12AH batteries. Many installations are charged by solar cells and this means a separate regulator is not required.

3. Convenient DIN Rail Mount. All modules are provided with a DIN rail mount clip which allows the whole unit to be mounted or removed quickly.

4. Special smartBase Modules. smartBase 1, the basic module is very capable. However other versions of the module add the ability to interface voltage and current sensors, rain gauges and solenoid valve outputs to the probeLink network. These are in development at present. It is possible to add several smartBase modules to the one installation using a simple daisy chain cable which plugs them together.

5. Inbuilt RS232 Connector. The smartBase 1 contains a 9 way RS232 D connector for standard RS232 communications. This allows the user to connect a PC or modem and communicate with the probeLink device.

6. Rugged and Compact Design. The module is based on a 100 * 50 mm footprint which can readily be mounted in small enclosures.

If the smartBase module is used in conjunction with probeLink, then connect the probeLink to the first 3 way terminal. There is a 470R resistor between the SDI-12 data line on this connection and the others, as required by the SDI-12 specification for sensors. Also it is possible to set the power supply to the other terminals to be shut off in some circumstances. Obviously the power to the probeLink should never be turned off.




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