Hardware channel selection

This window sets the links between the 'logical' channel and a physical connector to the analog-to-digital converter (UI2, DataTaker, ADC-1, etc.).  You can select any of the A to D channels that are available, in any order; you may also assign a single hardware input to several logical channels.
            The A to D INPUT window looks more-or-less like this example for the Sable UI2; the number of available inputs and other options depend on the specific A-D converter in use.

Here, four voltage inputs (including input 10, or T2, set at volts) and one temperature input (input 9; T1) have been selected.   Several other inputs are available.

  • Note:  When using the ADC-1, you can set each channel to automatically adjust the gain function to maximize resolution (the default mode), or to use a fixed gain (of 1 or 50).  The latter option is slightly faster.

    Special considerations:

  • Electrical connections to the A to D device should be mechanically solid and signals should be noise-free.   When using a DataTaker, the type of input (differential or single-ended, and in the latter case, which terminal is used) is important.

  • The number of hardware inputs varies with the device in use.   DataTakers have 5 (50-series), 10 (500- and 600-series) or 12 (DT800).  Importantly, on a DataTaker the inputs can be set to read temperature (thermocouples of various types) or voltages; a counter is also available.   You can connect more than one signal to each hardware input (up to 3).  Due to this complexity, hardware input selection on DataTakers includes this additional window that lets you spcify input parameters:

  • The ADAM-4019 has 8 inputs that can accept either voltages or thermocouples; you have a choice of voltage ranges (usually ±5 volts or ±2.5 volts will work well) and thermocouple types.
    Note that you can combine another ADAM module with a 4019:   either another 4019, or the 4017.   If you add a 4017, you will see 16 total inputs, but only the first 8 (from the 4019) have options for reading thermocouples -- the 4017 reads voltages only.   Hardware connectors specific to the second ADAM module are indicated by an asterisk (*) on the 'Input' selection button.

  • ADC-1s have 16 inputs.  The 'test mode' simulated converter also has 16.  The Sable UI2 and UI3 have 8 voltage inputs and 4 temperature inputs (for special thermistors); the 4 temperature inputs can also be set to read voltages or resistances; with an external board they can read another voltage input channel, a pulse counter, and a serial input channel.

  • With an ADC-1 you can specify automatic gain or fixed high (50X) or low (1X) gains.   The latter options are faster, but have a more limited range and resolution.   Use high gain only with voltages less than ±0.0082 V; use low gain only for voltages between ±0.42 and 0.0082 V.

  • Streaming serial input

     A number of Sable Systems instruments (and others) have serial ouputs; these send a fixed-format string of digital data directly to the computer, avoiding the need for an A-D converter.  Therefore the channel selection window discussed above does not appear.

    Usually, several different variables are sent in a serial stream. LabHelper knows the 'signatures' of some Sable instruments (the first part of the string contains an instrument ID), and can parse the string into the appropriate variables, with channel labels.

    In this example, from the Sable RH-100 humidty sensor, the device provides humidity as percent relative humidity, dew point, and vapor pressure; it also shows internal (cell) temperature. You need to pick one or more of these variables to record.

    • The 'Reload Data' button takes another reading from the instrument and updates the data fields.
    • The 'Add to Instrument Database' button lets you enter the correct data for an instrument that isn't recognized by LabHelper; these data are stored in a file called 'serial device data.txt'.

    Note that most Sable serial instruments update their serial strings only once or twice per second, so it's inadvisable to use this option at high sampling rates.

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