NI counter read task

Read frequency, edge counts, pulse widths, and encoder positions from NI counters into channels.

An NI counter read task reads the counter inputs of NI devices into channels. A counter measures digital pulses: their frequency, their count, their width, or the position and speed of an encoder. For example, it can record the speed of a flow meter on ctr0 of a USB-6343.

Before you start, you need configured devices.

Counters and timing

Each channel reads one counter, set by its Port: port 0 is ctr0. The pulses come in on a PFI terminal. Set Input terminal to choose the terminal, or leave it empty to use the default terminal of the counter. The device manual lists the counters and their terminals.

The Driver reads the counters on the computer clock, at the Sample rate. See timing.

Create an NI counter read task

import synnax as sy
from synnax import ni

dev = client.devices.retrieve(key="<device key>")
time = client.channels.create(
    name="dev1_ctr_time", is_index=True, data_type=sy.DataType.TIMESTAMP
)
flow = client.channels.create(
    name="flow_meter_hz", index=time.key, data_type=sy.DataType.FLOAT64
)

task = ni.CounterReadTask(
    name="Flow meter",
    device=dev.key,
    sample_rate=100,
    stream_rate=10,
    channels=[
        ni.CIFrequencyChannel(port=0, min_val=1, max_val=1000, channel=flow.key)
    ],
)
client.tasks.configure(task)
task.start()

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

const dev = await client.devices.retrieve({ key: "<device key>" });
const task = await client.tasks.create({
  name: "Flow meter",
  rack: dev.rack,
  type: "ni_counter_read",
  config: ni.counterReadConfigZ.parse({
    sampleRate: 100,
    streamRate: 10,
    channels: [
      {
        type: "ci_frequency",
        device: dev.key,
        port: 0,
        minVal: 1,
        maxVal: 1000,
        channel: flow.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, the counter number (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. The Console shows the same values in plain words. Every type except edge count 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

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

  Cause

  Two channels use the same counter 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.

• Cannot create task with channels from multiple racks

  Cause

  The channels use devices on two Drivers.

  Fix

  Create one task for each Driver.

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