ina2xx Current Sense devices for HydraFerret

HydraFerret: Multi-sensor IOT with a simple interface.


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Introduction

Current sense modules containing HydraFerret supported ina219, ina226, ina3221

The following table shows the supported sensors in this family and their characteristics. They work by measuring the voltage drop over a very small shunt resistor, typically in the range of 1 to 100 milliohms. The current does not pass through the sensor which measures the voltage drop over the shunt resistor. Changing the shunt resistor will change the current which the device can sense. Use the highest value shunt resistor which will cover the range of amps your device is expected to measure.


 ina219ina226ina3221
Input Channels113
Max Volts263626
Max Amps3.2770.8191.638
Resolution step mA0.1000.0250.400
Shunt Resistor Milli-Ohms:
Decimal points:
 

Since the ina3221 presents 3 channels to HydraFerret, each ina3221 is represented as 3 separate sensors. This allows each channel to potentially have a different value shunt resistor. Separate warning and critical alarms can be configured for each channel.

Note the ina226 has a separate "bus voltage" input which makes it use for both high-side and low-side current measurement. The other units are better used for high side only measurement, unless bus voltage and watts are not of interest. In high-side measurement the current sensor is place between the positive power source and the load. In low-side measurement the currrent sonsor is place between the load and ground. The ina226 also supports higher bus voltages and has the finest granularity of resolution of the supported devices.

Configuration

critical|extreme|warning ina2xx <0-n> [volt|amps|watt] disable
critical|extreme|warning ina2xx <0-n> [volt|amps|watt] <rpn-expression>
    enable or disable alerting thresholds on sensors

devicename ina2xx <0-n> <device-name>
    Name a sensor device, use "inventory" to list device types

i2c [<0-1> <sda> <scl> [speed]]
    Set i2c pins, eg: 21 and 22 for bus-0, and 5 and 4 for bus-1

interval [ina2xx <seconds>]
    Set the interval between measurements taken by the sensor.

resistor [ina2xx <index> <milliohm>]
    Set resistance of shunt resistor for voltage measurement

rpn variables:
    ina2xx.dev  - count of ina2xx family of sensors (DEVice count)
    ina2xx.volt - Voltage (5 minute average)
    ina2xx.lasv - Last voltage reading
    ina2xx.shun - Shunt resistor voltage drop (5 minute average
    ina2xx.lass - Last shunt resistor voltage drop
    ina2xx.amps - Amps (5 minute average)
    ina2xx.lasa - Last amps reading
    ina2xx.watt - Watts (5 minute average)
    ina2xx.lasw - Last watt reading
    ina2xx.resi - shut resistor in milliohm
    ina2xx.blsb - Sensitivity: volts per bit (bus)
    ina2xx.slsb - Sensitivity: millivolts per bit (shunt)
    ina2xx.fsd  - Full scale deflection for amps (max current reading)




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