CHESTER Current

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

caution

Some of the basics are not provided, as they are common for all CHESTER catalog applications. For example, see the chapter 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-K) 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).

The measurements are taken regularly as specified by the measurement-interval parameter. The measurements are stored in the measurement buffer and sent when the report interval expires (set by the report-interval parameter).

caution

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

Hardware Description

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

• CHESTER-M-CGLS
• CHESTER-K-C1-C2-C3-C4
• CHESTER-Z
• CHESTER-E2-LP

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

• Maximum current 10 A
• Maximum current 100 A
• Maximum current 500 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.

info

Upon request, it is possible to order a CHESTER Current variant without the CHESTER-Z module, and with the battery holder for the LiSoCl₂ primary cell on the mainboard. When configured properly, the CHESTER Current application can operate from the primary cell for several years.

Default Configuration

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

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

Specific Commands

info

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

Command to trigger measurement immediately (and store the result in the buffer of measurements):

measure

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

send

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

app config channel-active <n> <{false|true}>

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

app config channel-differential <n> <{false|true}>

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>

Example JSON Message

{
  "frame": {
    "protocol": 1,
    "sequence": 1,
    "timestamp": 1659967456
  },
  "attribute": {
    "vendor_name": "HARDWARIO",
    "product_name": "CHESTER-M",
    "hw_variant": "CGV",
    "hw_revision": "R3.2",
    "fw_version": "v1.0.0",
    "serial_number": "2159018442"
  },
  "state": {
    "uptime": 276
  },
  "battery": {
    "voltage_rest": 4.7,
    "voltage_load": 4.65,
    "current_load": 46
  },
  "network": {
    "imei": 351358815499600,
    "imsi": 901288910015788,
    "parameter": {
      "eest": 7,
      "ecl": 0,
      "rsrp": -82,
      "rsrq": -5,
      "snr": 11,
      "plmn": 23003,
      "cid": 1011233,
      "band": 20,
      "earfcn": 6447
    }
  },
  "thermometer": {
    "temperature": 27
  },
  "accelerometer": {
    "acceleration_x": 0,
    "acceleration_y": -0.16,
    "acceleration_z": 9.27,
    "orientation": 2
  },
  "measurements": [
    {
      "timestamp": 1659967264,
      "channel_1_avg": -1232,
      "channel_1_rms": 7545,
      "channel_2_avg": 199411,
      "channel_2_rms": 199504,
      "channel_3_avg": 2463,
      "channel_3_rms": 7338,
      "channel_4_avg": null,
      "channel_4_rms": null
    },
    {
      "timestamp": 1659967324,
      "channel_1_avg": -2104,
      "channel_1_rms": 7756,
      "channel_2_avg": 199277,
      "channel_2_rms": 199378,
      "channel_3_avg": 1827,
      "channel_3_rms": 7579,
      "channel_4_avg": null,
      "channel_4_rms": null
    }
  ]
}

Channel Calibration

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 measure 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.