ERT-A2 ALERT2 Configuration Manual
Revision 1.0
10
Sensor Input Connections
The ERTA2 unit can be connector to several different types of external sensor inputs such as discrete
on/off, pulsed, 4-20mA analog and SDI-12, allowing a large number of different sensors to be
monitored in a single installation.
There are several internal sensor inputs to allow diagnostic data to be transmitted or logged for
battery health, power supply or solar, communications status and internal temperature.
Type
Number
Configurations
Discrete
4
Pulsed, ON/OFF or encoder configurable
Analog
2
4-20mA
SDI-12
1 Channel
Up to max of 52 sensors and/or variables
Internal
4
Battery Voltage, Supply/Solar Voltage, Radio Received Signal
Strength, Internal Temperature, Internal Status
The ERTA2 is available in two enclosure options for support different types of installations. Mil Spec
connector enclosure provides a compatible connection with existing tree installations.
Cable gland enclosure option is available for installations where the Mil Spec connections are not
required and is a very good option for outdoor pole mounting, elevated platforms or cabinet
installations.
Digital or Pulsed inputs
Digital Input channel 1 & 2 on the module modules can be used for a digital ON/OFF signal, a pulsed
signal from something like a Tipping Bucket Rain Gauge, or a Shaft Encoder for measuring level.
In normal flood or environmental gauging applications digital Input 1 & 2 are used for a shaft
Encoder. Shaft Encoders translate the rotation of an input shaft into a digital signal which can be
read in the ERT-A2 inputs. A float connected to a beaded line over a pulley causes the shaft to rotate
as it rises and falls with river level. Shaft encoders generally use some sort of "stilling well" in the
river so that waves on the surface of the river do not cause the encoder to continually fluctuate. The
ERTA2 unit supports incremental or quadrature type shaft encoders.
Digital Input 3 is a Pulsed input signal only, normally used for a Tipping Bucket Rain Gauge (TBRG)
providing a dry contact closure through a small magnetic switch triggering for each increment of rain
fall. Maximum Pulsed input rate is 10Hz
Digital Input 4 can only be used as Digital ON/OFF input, which could be used for a limit switch or
intruder alarm.
The digital inputs whether a pulse, ON/OFF switch or encoder are activated by connecting the input
terminal to GND or common, either by voltage free contact, TTL level, or transistor switch.
Analog inputs
The module provides two floating differential analog inputs capable of measuring 0-24mA for 4-
20mA transducers/sensors.
It should also be noted that the analog inputs can also be used to connect single ended current
sinking or sourcing devices and can be connected in top or bottom of the analog loop.
The module also provides a switched 24V Analog Loop Supply (ALS) with a maximum of 50mA for
any single ended current loops. To get the best battery life performance the ALS can be configured
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