ITU G2 Physical Characteristics
- Width = 171mm
- Height = 121mm
- Depth = 77mm
- Mass = 621g
Top of page
- Power and I/O: Pluggable rising clamp style screw terminal. Wire capacity up to 2.0mm diameter. (Dinkle style 5ESDV)
- Data: Female 9-pin D-connector
- Antennas: SMA Jack (female, 50 Ohm ).
- Wind sensor: Vertical RJ11 style modular telephone jack. Six way body with four contacts fitted. Connections are duplicated on a pluggable screw terminal block.
- Auxiliary ports: 2mm pitch vertical header (JST part B4B-PH-K-S).
The power and I/O connections are divided across five pluggable terminal blocks each of a different size. Analog inputs and wind sensor connections are an a sixteen way block. Excitation outputs are on a six way block. Power is on a four way block. Relay contacts, SDI-12, and 1-Wire sensor connections are on a thirteen way block. Digital inputs are on a twelve way block.
- Carrier Detect
- Receive Data
- Transmit Data
- Data Terminal Ready
- Signal Ground
- Data Set Ready
- Ready To Send
- Clear To Send
- Ring Indicator
- Power output
- Transmit Data (from ITU)
- Receive Data (to ITU)
The auxiliary connectors have a power output that can be configured via jumper setting to provide power at 3.3V, 5.2V or unregulated (typically 12V). The transmit data output provides a 0 to 5V logic level output. The receive data input is compatible with 0 to 3.3V or 0 to 5V logic levels or RS-232 levels. Data polarity for, both transmit and receive, may be configured via jumper to be either positive mark (typical logic levels) or positive space (like RS-232).
- No contact
- Direction excitation (Exc)
- Direction wiper (Dir)
- Common (Gnd)
- Speed pulses (Speed)
- No contact
Wind sensor connections are duplicated on pluggable screw terminals. Screw terminal labelling is shown in parenthesis in the table above.
Top of page
There are eight digital inputs designed for detecting contact closures. As shown in the schematic below, each digital input circuit is based around a BC857 PNP transistor with its emitter connected to 3.3V. A 27kΩ resistor is connected between the base and emitter and a second 27kΩ resistor is connected between the base and the external digital input port.
The maximum pull down external contact resistance is 29kΩ. For devices with outputs that are not purely resistive, such as transistor outputs, the input should be pulled down to 1.2V or less. The minimum open circuit pull down resistance is 250kΩ or 2.7V.
Direct connection of external voltage sources is not recommended but could be accommodated by using an external voltage divider.
The eight analog inputs can be software configured for full scale input ranges of 2.048V, 10.24V, 40.96V, or 20.48mA. These are refered to as 2V, 10V, 40V, and 4-20mA. Input impedances for the 10V and 40V ranges are 50kΩ and 200kΩ respectively. The 2V range is a high impedance input with an input bias current of less than 200pA. The 4-20mA range has an input impedance of 100Ω so this results in a voltage burden of 2V at 20mA.
The RJ11 style modular jack for the wind sensor provides a convient connection for the wind sensor used on Harvest weather stations. All the connections on this connector are in parallel with screw terminals connections so the screw terminals may be used as an alternative to accomodate different wind sensors. The direction excitation is a switched 2.048V output and is able to support wind direction potentiometers of 4k or greater. The speed input expects pulses in the form of a switch closure to ground.
The ITU_G2 has two inputs for Dallas 1-Wire bus sensors. Currently Harvest offers
temperature and humidity sensors that may be connected to these inputs.
Two latching relay outputs are provided. These are rated at 2A and 30V.
The ITU_G2 features an SDI-12 port conforming to SDI-12 version 1.3 section 3. For further information on SDI-12 see the SDI-12 Support Group.
Top of page
Four excitation outputs are available for supplying analog sensors. The operation of these outputs can be configured by ITU_G2 commands.
V1 and V2: DAC Outputs
The ITU_G2 has two programmable voltage outputs. These can be configured to between zero and 12.288V. The output voltage accuracy is better then 1.5% but the upper limit can be restricted by the supply voltage of the ITU. Each output is capable of delivering at least 1A but internal heat dissipation can reduce this limit. Heat dissipation is determined by the difference between the supply voltage and the output voltage multiplied by the load current and the duty cycle. The duty cycle is determined by the interval and delay parameters of the excitation configuration setting. If the duty cycle is below 5% or the load current is below 50mA then heat dissipation should not be a concern.
V3: 12V Output
This output is a switched unregulated output. The output voltage will depend on the input power and state of the battery. In addition, a voltage drop of up to 1V should be allowed for due to a diode and two MOSFETs in the ITU. Care should be taken to ensure that the worst case supply voltage will be sufficient to power any sensors attached to this output. Up to 1A may be drawn from this output.
V4: 15V Output
In some situations the 12V ouput may not always be high enough to meet a sensor's minimum voltage requirement. For this reason the ITU_G2 includes a regulated 15V output. This output uses a boost converter to generate the 15V output even then the supply voltage is significantly lower. Up to 100mA may be drawn from this output.
Top of page
The ITU_G2 is designed to be powered from a nominal 12V DC supply but can be operated from a supply voltage of between 10 and 15V DC. One of three standard power supply configurations may be used.
||Caution: The Harvest ITU_G2 must only be powered from an approved SELV power supply.
External DC supply
A external DC supply of between 10 and 15V may be conneted to the Gnd and Batt+ connections of the Power In connector. Nothing should be connected to the Solar connection. The external supply must be able to deliver the peak current required by the ITU plus any attached sensors.
Solar Panel + Battery
A 12V valve regulated lead acid (aka sealed lead acid) battery of 3.4Ah or greater capacity should be connected to the Gnd and Batt+ connections. A 12V solar panel of 5 to 20W capacity should be connected to the Solar and Gnd connections. A nominal 12V solar panel will typically have a peak open circuit voltage of around 21V and a peak power output at around 17V. The ITU_G2 battery charging circuit is a two stage charger: initially constant current and then switching to constant voltage once the battery reaches the float voltage. While constant current charging the ITU monitors the voltage of the solar panel and will restrict the battery charging current to keep the solar panel voltage close to 17V. Once the battery reaches float voltage the solar panel voltage may rise as more power is available than is needed.
External DC supply + Battery
An external DC supply of 15-30V may be connected in place of the solar panel. The ITU will then use this supply to charge the battery. For supplies below 17V it is necessary to remove the internal jumper labelled "Sol".
This configuration may also be used without a battery. Since the ITU (and external sensors) will then be powered from the external supply alone it is necessary to ensure that the external supply can delivery the maximum peak current that is required. As well as any limitation of the external supply the ITU battery charger may restrict the peak current to as low as 1.4A.
Due to the transmit bursts the ratio of peak to average current for any GSM phone is quite high. In testing we found the highest instantaneous peak current the ITU drew from a 12V supply was around 800mA.
The base current consumption of an ITU_G2 in low power mode with no terminal attached is about 60µA from a 12V supply. The average current consumption in real applications will be greater than this but how much greater will depend on configuration and settings.
Each digital input switched to ground will increase current consumption by approximately 155µA.
Changes in the level of analog input signals have no significant impact on the ITU power draw however the power drawn by the sensors needs to be considered. Naturally the power draw by the sensors themselves needs to be taken into account but also the ITU analog input impedance should be considered. For example: a sensor with an output of 10V output would have to supply 200µA to an ITU input configured for a 10V range of 50µA for a 40V input. The sampling intervals and delays of the excitation outputs can be used to manage the power consumption of sensors.
As shown in the table below, the RS-232 port can be a major contributor to power consumption. To save power in low power mode the RS-232 port is slept for about 98% of the time but even the remaining 2% can have a major impact on current consumption if care is not taken.
|RS-232 port power usage|
|RS-232||Per pin, 3kΩ Load||4.4mA|
|RS-232||Per pin, 7kΩ Load||1.9mA|
|RS-232||5 pins, 3kΩ Load||22.0mA|
|RS-232||5 pins, 7kΩ Load||9.5mA|
Top of page