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CHESTER Current

This article describes the core functionality, hardware description, default configuration, example JSON message, and channel calibration of the catalog application CHESTER Current.

danger

When upgrading firmware from v1.x.x to version v2.0.0 and newer - it is necessary to backup configuration. In the case of using CHESTER Current also calibration data.

caution

Some of the basics are not provided, as they are common for all CHESTER catalog applications. For example, see the article Platform Management on how to work with the interactive console.

Application Overview​

The application primarily targets non-invasive current measuring using the so-called DC Current "Transformer" (DCCT). It can measure up to 4 channels of both AC and DC currents. The current probes are clips around the measured line, which convert the magnetic flux (proportional to the electrical current) to a differential output voltage.

tip

The current probes require a 5 V power supply (generated using the boost converter on CHESTER-K1) during the measurement cycle. The boost converter and the power rails to each channel are software-controlled, so CHESTER Current can operate as a low-power device powered by the battery. Of course, the measurement interval plays a key role in the battery lifespan.

Apart from the current measurements, the device can be configured (on demand) to measure up to 4 voltage channels (in single-ended mode). It can combine both current and voltage measurements (the total number of channels never exceeds number 4).

Application Variants​

CHESTER Current can be ordered in one of these variants:

CHESTER Current​

The catalog CHESTER Current hardware consists of the following ordering codes:

  • CHESTER-M-CGLS - Standard mainboard
  • CHESTER-K1-C1-C2-C3-C4 - 4x Diff. Input + 5 V Boost
  • CHESTER-E2-LP - Enclosure with SMA pigtail

See Ordering Codes for more details.

Firmware build shield options: ctr_k1 ctr_lte

CHESTER Current Z​

The catalog CHESTER Current Z hardware consists of the following ordering codes:

  • CHESTER-M-CGLS - Standard mainboard
  • CHESTER-K1-C1-C2-C3-C4 - 4x Diff. Input + 5 V Boost
  • CHESTER-Z1 - Backup module
  • CHESTER-E2-LP - Enclosure with SMA pigtail

See Ordering Codes for more details.

Firmware build shield options: ctr_k1 ctr_lte ctr_z

CHESTER Current 1W​

The catalog application CHESTER Current 1W supports multiple external DS18B20 1-Wire temperature sensors.

The hardware of this application consists of the following ordering codes:

  • CHESTER-M-CGLS - Standard mainboard
  • CHESTER-K1-C1-C2-C3-C4 - 4x Diff. Input + 5 V Boost
  • CHESTER-E2-LP - Enclosure with SMA pigtail

See Ordering Codes for more details.

Firmware build shield options: ctr_ds18b20 ctr_k1 ctr_lte

Probes​

You can choose up to 4 current probes with the following current ranges:

  • Maximum current 10 A
  • Maximum current 100 A
  • Maximum current 300 A
  • Maximum current 1.000 A
  • Maximum current 1.500 A
caution

The current range is specified for the DC. If you design your system for the AC, you have to multiply the maximum expected AC by the coefficient of 1.42 (square root of two) to see if the current probe fits within the limit.

Application Behavior​

For the wiring diagram to CHESTER Current, please follow the terminal block description of the CHESTER-K1 extension module. The extension module CHESTER-K1 use both slots A and B. So you use the corresponding terminals A1 to A8 and B1 to B8.

Analog​

  • The analog readings are sampled periodically (parameter channel-interval-sample). These readings are stored as a buffer of samples.

  • The collected samples are aggregated periodically (parameter channel-interval-aggreg). The minimum, maximum, average, and median aggregates are computed from the buffered samples. These aggregated results are referred to as measurements.

  • Each measurement has an associated timestamp. The buffer measurements are transferred as time-series data regularly (parameter interval-report).

Backup​

CHESTER Current Z (equipped with CHESTER-Z1) can also report information on the backup battery and external DC power state.

  • The current battery voltage and external DC voltage are sent in every report.

  • When the DC power input changes, the timestamp of the change event is stored altogether with the connected/disconnected state, this information is buffered, and the buffer of the events is sent (at the latest) with the regular report (parameter interval-report).

  • Optionally, DC power input changes to the connected (parameter backup-report-connected) or disconnected (parameter backup-report-disconnected) states can be reported immediately or with a configurable delay (parameter event-report-delay) to allow capturing multiple consequent input changes.

  • The maximum number of reports per hour is configurable (parameter event-report-rate). The event throttling limits communication bandwidth and preserves the battery lifespan.

caution

The next report interval is calculated at the beginning of the transmission cycle as the interval-report parameter (specified in seconds) ±20 % spread. This spread is intentionally random to avoid transmission aliasing for multiple devices operating in the same place (e.g., powered from a local DC line). If such a spread was not implemented, the device transmission could synchronously overlap.

Default Configuration​

This is the default configuration (printed using the app config show command):

app config interval-report 900
app config event-report-delay 1
app config event-report-rate 30
app config backup-report-connected true
app config backup-report-disconnected true
app config channel-interval-sample 60
app config channel-interval-aggreg 300
app config channel-active 1 false
app config channel-active 2 false
app config channel-active 3 false
app config channel-active 4 false
app config channel-differential 1 false
app config channel-differential 2 false
app config channel-differential 3 false
app config channel-differential 4 false
app config channel-calib-x0 1 0
app config channel-calib-x0 2 0
app config channel-calib-x0 3 0
app config channel-calib-x0 4 0
app config channel-calib-y0 1 0
app config channel-calib-y0 2 0
app config channel-calib-y0 3 0
app config channel-calib-y0 4 0
app config channel-calib-x1 1 0
app config channel-calib-x1 2 0
app config channel-calib-x1 3 0
app config channel-calib-x1 4 0
app config channel-calib-y1 1 0
app config channel-calib-y1 2 0
app config channel-calib-y1 3 0
app config channel-calib-y1 4 0
app config w1-therm-interval-sample 60
app config w1-therm-interval-aggreg 300

Specific Commands​

info

You can easily explore the whole command tree structure - start with the help command.

Commands​

Command to trigger sample immediately (and store the result in the sample buffer):

sample

Command to send data immediately (and flush the aggregated measurements):

send

Reporting​

Use this command to set report interval (in seconds):

app config interval-report <value>

Backup​

Use this command to configure a short delay (in seconds) between the backup event and its reporting:

app config event-report-delay <value>
tip

This feature is useful in systems where another change may arrive shortly after the first one.

Use this command to limit the number of asynchronous backup event reports in a one-hour window:

app config event-report-rate <value>
tip

This feature helps to conserve power in the battery-operated device and optimizes the amount of transferred data. The regular (periodic) reports set by the parameter interval-report are not counted to this limit.

Use these commands to enable/disable reporting of the backup module power input connect/disconnect events:

app config backup-report-connected <true/false>
app config backup-report-disconnected <true/false>

Analog Channels​

Command to enable/disable channel n (index 1-4):

app config channel-active <n> <true/false>

Command to switch between single-ended/differential modes on the channel n (index 1-4):

app config channel-differential <n> <true/false>

Command to set calibration point X0 (input) on the channel n (index 1-4):

app config channel-calib-x0 <n> <value>

Command to set calibration point Y0 (output) on the channel n (index 1-4):

app config channel-calib-y0 <n> <value>

Command to set calibration point X1 (input) on the channel n (index 1-4):

app config channel-calib-x1 <n> <value>

Command to set calibration point Y1 (output) on the channel n (index 1-4):

app config channel-calib-y1 <n> <value>

1-Wire Thermometer​

Command to set 1-Wire thermometer sample interval in seconds:

app config w1-therm-interval-sample <1-86400>

Command to set 1-Wire thermometer aggregate interval in seconds:

app config w1-therm-interval-aggreg <1-86400>

Firmware​

danger

When upgrading firmware from v1.x.x to version v2.0.0 and newer - it is necessary to backup configuration. In the case of using CHESTER Current also calibration data.

The latest firmware is available in Catalog Applications Firmware chapter.

Example JSON Message​

{
  "message": {
    "version": 1,
    "sequence": 1,
    "timestamp": 1673272805
  },
  "attribute": {
    "vendor_name": "HARDWARIO",
    "product_name": "CHESTER-M",
    "hw_variant": "CDGLS",
    "hw_revision": "R3.2",
    "fw_name": "CHESTER Current",
    "fw_version": "v1.5.0",
    "serial_number": "2159018247"
  },
  "system": {
    "uptime": 131,
    "voltage_rest": 4.73,
    "voltage_load": 4.67,
    "current_load": 46
  },
  "backup": {
    "line_voltage": 9.51,
    "batt_voltage": 3.45,
    "state": "connected",
    "events": []
  },
  "network": {
    "imei": 351358815178303,
    "imsi": 901288003957939,
    "parameter": {
      "eest": 7,
      "ecl": 0,
      "rsrp": -87,
      "rsrq": -4,
      "snr": 16,
      "plmn": 23003,
      "cid": 939040,
      "band": 20,
      "earfcn": 6447
    }
  },
  "thermometer": {
    "temperature": 22.68
  },
  "accelerometer": {
    "acceleration_x": -0.16,
    "acceleration_y": 0.07,
    "acceleration_z": 9.88,
    "orientation": 2
  },
  "analog_channels": [
    {
      "channel": 1,
      "measurements": [
        {
          "timestamp": 1673272718,
          "mean_min": 1037,
          "mean_max": 1039,
          "mean_avg": 1038,
          "mean_mdn": 1038,
          "rms_min": 1037,
          "rms_max": 1039,
          "rms_avg": 1038,
          "rms_mdn": 1038
        },
        {
          "timestamp": 1673272748,
          "mean_min": 1038,
          "mean_max": 1038,
          "mean_avg": 1038,
          "mean_mdn": 1038,
          "rms_min": 1038,
          "rms_max": 1038,
          "rms_avg": 1038,
          "rms_mdn": 1038
        },
        {
          "timestamp": 1673272778,
          "mean_min": 1038,
          "mean_max": 1038,
          "mean_avg": 1038,
          "mean_mdn": 1038,
          "rms_min": 1038,
          "rms_max": 1038,
          "rms_avg": 1038,
          "rms_mdn": 1038
        }
      ]
    },
    {
      "channel": 2,
      "measurements": [
        {
          "timestamp": 1673272718,
          "mean_min": 0,
          "mean_max": 0,
          "mean_avg": 0,
          "mean_mdn": 0,
          "rms_min": 0,
          "rms_max": 0,
          "rms_avg": 0,
          "rms_mdn": 0
        },
        {
          "timestamp": 1673272748,
          "mean_min": 0,
          "mean_max": 0,
          "mean_avg": 0,
          "mean_mdn": 0,
          "rms_min": 0,
          "rms_max": 0,
          "rms_avg": 0,
          "rms_mdn": 0
        },
        {
          "timestamp": 1673272778,
          "mean_min": 0,
          "mean_max": 0,
          "mean_avg": 0,
          "mean_mdn": 0,
          "rms_min": 0,
          "rms_max": 0,
          "rms_avg": 0,
          "rms_mdn": 0
        }
      ]
    },
    {
      "channel": 3,
      "measurements": [
        {
          "timestamp": 1673272718,
          "mean_min": -8,
          "mean_max": -7,
          "mean_avg": -8,
          "mean_mdn": -8,
          "rms_min": 8,
          "rms_max": 8,
          "rms_avg": 8,
          "rms_mdn": 8
        },
        {
          "timestamp": 1673272748,
          "mean_min": -8,
          "mean_max": -8,
          "mean_avg": -8,
          "mean_mdn": -8,
          "rms_min": 8,
          "rms_max": 9,
          "rms_avg": 8,
          "rms_mdn": 8
        },
        {
          "timestamp": 1673272778,
          "mean_min": -8,
          "mean_max": -8,
          "mean_avg": -8,
          "mean_mdn": -8,
          "rms_min": 9,
          "rms_max": 9,
          "rms_avg": 9,
          "rms_mdn": 9
        }
      ]
    },
    {
      "channel": 4,
      "measurements": [
        {
          "timestamp": 1673272718,
          "mean_min": 4,
          "mean_max": 5,
          "mean_avg": 4,
          "mean_mdn": 4,
          "rms_min": 5,
          "rms_max": 5,
          "rms_avg": 5,
          "rms_mdn": 5
        },
        {
          "timestamp": 1673272748,
          "mean_min": 4,
          "mean_max": 4,
          "mean_avg": 4,
          "mean_mdn": 4,
          "rms_min": 5,
          "rms_max": 5,
          "rms_avg": 5,
          "rms_mdn": 5
        },
        {
          "timestamp": 1673272778,
          "mean_min": 4,
          "mean_max": 4,
          "mean_avg": 4,
          "mean_mdn": 4,
          "rms_min": 5,
          "rms_max": 5,
          "rms_avg": 5,
          "rms_mdn": 5
        }
      ]
    }
  ],
  "w1_thermometers": [
    {
      "serial_number": 170783697,
      "measurements": [
        {
          "timestamp": 1673272718,
          "min": 21.25,
          "max": 21.25,
          "avg": 21.25,
          "mdn": 21.25
        },
        {
          "timestamp": 1673272748,
          "min": 21.25,
          "max": 21.31,
          "avg": 21.27,
          "mdn": 21.25
        },
        {
          "timestamp": 1673272778,
          "min": 21.25,
          "max": 21.25,
          "avg": 21.25,
          "mdn": 21.25
        }
      ]
    },
    {
      "serial_number": 170787196,
      "measurements": [
        {
          "timestamp": 1673272718,
          "min": 21.43,
          "max": 21.43,
          "avg": 21.43,
          "mdn": 21.43
        },
        {
          "timestamp": 1673272748,
          "min": 21.43,
          "max": 21.43,
          "avg": 21.43,
          "mdn": 21.43
        },
        {
          "timestamp": 1673272778,
          "min": 21.43,
          "max": 21.43,
          "avg": 21.43,
          "mdn": 21.43
        }
      ]
    }
  ]
}

Channel Calibration​

danger

When upgrading firmware from v1.x.x to version v2.0.0 and newer - it is necessary to backup configuration. In the case of using CHESTER Current also calibration data.

caution

The following section is provided only for reference. Usually, the CHESTER Current devices are ordered altogether with the current probes, and HARDWARIO does the channel calibration for their customers in such a case.

In the CHESTER Current application, each channel can be individually calibrated using two-point calibration (two points specified by the XY coordinates). For these two points together with the input value (from the A/D converter), CHESTER performs the so-call linear interpolation.

tip

Linear interpolation is defined by this formula for output calculation:

y = y0 + (x - x0) * (y1 - y0) / (x1 - x0)

Where y is the output value, x is the input value (number read from the A/D converter), and the constants x0 + y0 + x1 + y1 represent the calibration points.

In HARDWARIO, we have a calibration kit for CHESTER Current made of several air-core coils with 10/50/100 turns.

Example Current Calibration​

  1. Measure the zero-current offsets and write them for each channel as the x0 parameter

    tip

    Use the sample command to trigger the measurement.

  2. Let's assume calibration of 100 A current probe and pick the 100-turn coil.

  3. Set the laboratory power supply's current limit to 900 mA, and connect the power supply to the coil.

  4. Clip the current probe around the calibration coil.

  5. Verify the current flowing to the coil using a multimeter connected in series.

  6. Measure the channel, and write the reading as the x1 value.

  7. Set the y1 parameter to the value 90000.

    info

    The value represents the multiplication of the number of turns on the coil and the power supply's current limit - in this example 90000.

  8. Since we assumed a zero-current offset point, we can keep the x0 parameter set as 0.

  9. Save the configuration data (using the config save command) and verify the applied calibrated values.