NI analog read task

Read voltages, currents, temperatures, and other sensor signals from NI devices into channels.

An NI analog read task reads the analog inputs of NI devices into channels. Each channel has a type, such as voltage, current, thermocouple, or bridge, and NI-DAQmx converts the signal to the units of that type. For example, one task can record pressure transducers on an NI 9205 and thermocouples on an NI 9211 in the same chassis.

Before you start, you need configured devices.

Channels and timing

Each channel reads one port of one device. A task can use the modules of one chassis, and all of them must be on the same Driver. The task samples every channel on the device clock, at the Sample rate. See timing.

Only one running task can use the analog inputs of a module. A second task on the same module fails to start with an NI-DAQmx error that says the resource is reserved.

Create an NI analog read task

import synnax as sy
from synnax import ni

dev = client.devices.retrieve(key="<device key>")
time = client.channels.create(
    name="dev1_ai_time", is_index=True, data_type=sy.DataType.TIMESTAMP
)
pressure = client.channels.create(
    name="tank_pressure", index=time.key, data_type=sy.DataType.FLOAT32
)

task = ni.AnalogReadTask(
    name="Tank sensors",
    device=dev.key,
    sample_rate=1000,
    stream_rate=25,
    channels=[
        ni.AIVoltageChannel(
            port=0, min_val=-10, max_val=10, channel=pressure.key
        ),
    ],
)
client.tasks.configure(task)
task.start()

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

const dev = await client.devices.retrieve({ key: "<device key>" });
const time = await client.channels.create({
  name: "dev1_ai_time",
  isIndex: true,
  dataType: "timestamp",
});
const pressure = await client.channels.create({
  name: "tank_pressure",
  index: time.key,
  dataType: "float32",
});

const task = await client.tasks.create({
  name: "Tank sensors",
  rack: dev.rack,
  type: "ni_analog_read",
  config: ni.analogReadConfigZ.parse({
    sampleRate: 1000,
    streamRate: 25,
    channels: [
      {
        type: "ai_voltage",
        device: dev.key,
        port: 0,
        minVal: -10,
        maxVal: 10,
        channel: pressure.key,
      },
    ],
  }),
});
await task.start();

Tare channels

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

1. In the channel list, click Tare on a 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

Every channel has a channel, the Synnax channel that records the value, a device, the key of the device (Device), and a port (Port). The built-in temperature sensor has no port. In Python, a channel with no device uses the device of the task.

Each table shows the Console label of a setting, with its Python field under it. The Notes column lists the values that code uses, such as MetersPerSecondSquared. The Console shows the same values as symbols, such as m/s². Every type except the temperature types also has Custom scaling.

Custom scaling

Channels with Custom scaling convert the raw value before the Driver writes it. In the Console, the options are in the Scale section of the channel. In code, set custom_scale to one of these scales:

Every scale except None also has Prescaled units (pre_scaled_units, Volts) and Scaled units (scaled_units).

Troubleshooting

• configured sample rate ... is below device minimum ...

  Cause

  The device cannot sample that slowly.

  Fix

  Raise the Sample rate to at least the minimum in the description.

• The task does not start, with an error that says the resource is reserved.

  Cause

  Another running task uses the analog inputs of the same module.

  Fix

  Stop the other task, or move its channels into this task.

• Port ... has already been used on another channel on the same device

  Cause

  Two channels use the same port of one device.

  Fix

  Change the port of one of them.

• No device provided for channel ...

  Cause

  A Python channel has no device, and the task has no device either.

  Fix

  Set one of them.

• The network cannot keep up with the stream rate.

  Cause

  The Driver cannot send the samples fast enough. The task shows “Failed to read data”, with this text in the description.

  Fix

  Lower the Stream rate, so that each batch holds more samples.

For other problems, see Configure an NI device and Troubleshoot hardware.