LabJack read task

Read analog, digital, and thermocouple inputs from a LabJack into channels.

A LabJack read task reads the inputs of one LabJack device into channels. For example, it can record a pressure transducer on AIN0 and a switch on DIO4 at 1 kHz.

Before you start, you need a configured device.

Channels and timing

A read task has three types of channels:

• Analog input -> a voltage on an AIN port.
• Digital input -> the state of a DIO port, as 0 or 1.
• Thermocouple -> a temperature from a thermocouple on an AIN port. Thermocouples work on the T7 and the T8.

A task streams: the device samples the inputs on its own clock. A T7 task with thermocouple channels polls instead: the Driver reads one sample of each channel at a time, on its own clock. See timing.

A T8 task with thermocouple channels samples at 250 Hz or less. It needs T8 firmware 1.0038 or later and LJM 1.2304 or later.

A LabJack runs one stream at a time and cannot read AIN ports during a stream, so a streaming task must be the only read task on its device. Add more channels to that task instead of starting a second one.

Create a LabJack read task

import synnax as sy
from synnax import labjack

dev = client.devices.retrieve(key="<serial number>")
time = client.channels.create(
    name="lj1_time", is_index=True, data_type=sy.DataType.TIMESTAMP
)
pressure = client.channels.create(
    name="lj1_AIN0", index=time.key, data_type=sy.DataType.FLOAT32
)
switch = client.channels.create(
    name="lj1_DIO4", index=time.key, data_type=sy.DataType.UINT8
)

task = labjack.ReadTask(
    name="Test stand inputs",
    device=dev.key,
    sample_rate=1000,
    stream_rate=25,
    channels=[
        labjack.AnalogReadChannel(port="AIN0", channel=pressure.key),
        labjack.DigitalReadChannel(port="DIO4", channel=switch.key),
    ],
)
client.tasks.configure(task)
task.start()

import { labjack } from "@synnaxlabs/client";

const dev = await client.devices.retrieve({ key: "<serial number>" });
const time = await client.channels.create({
  name: "lj1_time",
  isIndex: true,
  dataType: "timestamp",
});
const pressure = await client.channels.create({
  name: "lj1_AIN0",
  index: time.key,
  dataType: "float32",
});

const task = await client.tasks.create({
  name: "Test stand inputs",
  rack: dev.rack,
  type: "labjack_read",
  config: labjack.readConfigZ.parse({
    device: dev.key,
    sampleRate: 1000,
    streamRate: 25,
    channels: [{ type: "analog", port: "AIN0", channel: pressure.key }],
  }),
});
await task.start();

Tare channels

Tare sets the current value of an analog channel to zero. The task must be running.

1. In the channel list, click Tare on an analog channel. To tare several channels, select them, right-click, and select Tare.
2. The values of those channels start from zero.

Task options

Channel reference

Each channel has a channel, the Synnax channel that records the value. Each table shows the Console label of a setting, with its Python field under it.

Troubleshooting

• Falling behind hardware

  Cause

  The Driver cannot send the samples as fast as the device makes them.

  Fix

  Lower the Stream rate, or lower the Sample rate.

• Skipped samples

  Cause

  The buffer of the device filled, so the device skipped samples. The Driver writes no value for a skipped sample.

  Fix

  Lower the Sample rate, or check the USB cable or the network.

• Thermocouple out of range

  Cause

  The voltage of the thermocouple is outside the range of its Thermocouple type. The thermocouple is open, a wire is loose, or the type is wrong. The Driver writes NaN until the voltage is in range.

  Fix

  Check the wires of the thermocouple and its Thermocouple type.

• A T8 task with thermocouples samples at 250 Hz or less

  Cause

  Above 250 Hz, the T8 cannot read the temperature at its terminals, which the Driver needs to convert thermocouples.

  Fix

  Set the Sample rate to 250 Hz or less.

• Thermocouples on a T8 need firmware ... or later

  Cause

  The firmware of the T8 cannot stream the temperature at its terminals.

  Fix

  Update the firmware of the T8 with Kipling.

• Thermocouples on a T8 need LJM ... or later

  Cause

  The LJM library on the computer that runs the Driver cannot stream the temperature at the terminals of a T8.

  Fix

  Install the latest LJM, then restart the Driver.

• Using default calibration

  Cause

  The calibration constants of the device are not valid. LJM uses default constants, so readings may be inaccurate. The task continues to record data.

  Fix

  Contact LabJack support.

• ... is a thermocouple channel, but the T4 does not support thermocouples.

  Cause

  The T4 has no thermocouple inputs.

  Fix

  Use a T7 or a T8 for thermocouple channels.

• ... is a thermocouple channel, so it cannot be the CJC source of ...

  Cause

  The CJC source of a thermocouple is the port of another thermocouple channel. A thermocouple port has no CJC sensor.

  Fix

  Set CJC source to Device, or to the AIN port of a CJC sensor.

• ... has a max voltage of ..., but the largest range of the device is ...

  Cause

  The Max voltage of the channel is larger than the largest input range of the device: ±10 V on a T7, and ±11 V on a T8.

  Fix

  Lower the Max voltage of the channel.

• A T7 task fails to start after a change to Max voltage.

  Cause

  On a T7, a small range takes longer to settle. A task with more than one channel and a Max voltage of 1 V or less can then not stream at its Sample rate.

  Fix

  Lower the Sample rate, or set Max voltage back to 10. See LabJack’s stream rates.

• Port ... has already been used on another channel

  Cause

  Two channels use the same port.

  Fix

  Select a different port for one of them.

For other problems, see Configure a LabJack device and Troubleshoot hardware.