Define Instruments provides innovative solution to plant breeding research centre

January 2015 News

Agri Seeds Research Centre in Canterbury, New Zealand, commissioned Define Instruments to provide a wireless link between a reservoir and a pump station. The link was required so that the reservoir’s level sensor could communicate with the pump controller to maintain a consistent water level.

But there was a complication, a site evaluation showed that there was no line of sight between the reservoir and the pump station and that there were significant RF obstacles in the form of large trees and buildings. Taking these into account, it was decided to install a Define Instruments Twin Link (point to point) wireless system.

To achieve a successful link three devices were required: the Twin Link I/O pair plus a repeater unit.

The P2P-I unit takes two isolated input signals which include temperature sensors, process inputs, and frequency, as well as four digital inputs. In this case it was used to measure a single 4-20 mA output signal from the reservoir level sensor.

This analogue signal was converted to a digital message and transmitted to the repeater, which automatically forwards it to the P2P-O unit. This then reconstructs the original 4-20 mA signal which is wired to the pump controller.

“Commissioning the system was straight forward,” said installer John Green. “The radio system is based on Zigbee technology and is thus self-configuring. Within minutes of going live the system was functioning, however, we noted from the input unit’s LEDs that the RF signal link quality was poor.

“To overcome this we changed the antennas to higher gain versions to punch through the obstacles. Once this was done the signal link quality LED’s indicated maximum quality and we were confident that we had achieved a reliable setup for our customer.”

Define Instruments Rolla Afrogheh explained that it would also be possible to reduce costs in a new installation by programming the input device to control the pump directly, removing the need for a separate pump controller. The digital inputs and outputs are transparently transmitted between the input and output devices. So in the case where the input is setup as a controller, the output relay states are automatically routed to the output device’s relays.

For more information contact Dylan Swartz, Define Instruments South Africa, +27 (0)87 945 2700,,

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