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Making Alarm I/Os Smarter – Part 1

This new series of blog posts will highlight some of the more advanced features found in the new Optima NEXUS nano and RIO xR3 Remote Terminal Units (RTU).

The first installment provides a look at the analog input processing capabilities common to both models.

PART 1: ANALOG INPUTS

OVERVIEW

To offer improved flexibility, each analog input of the NEXUS nano and RIO xR3 RTUs can be programmed with a unique:

  • gain,
  • offset,
  • scale,
  • bias,
  • quantizer, as well as
  • upper, and
  • lower limits.

Each input can also have its own custom unit string. The output format is controllable as well.

This might look like a lot to take in but the following section will go through these step-by-step.

PARAMETERS

Amplifies small analog signals for better input range coverage. Spreading a small signal over a larger portion of the range available for the input will improve the fidelity and signal resolution. The following hardware GAIN stages are selectable:

1:1
1:2
1:4
1:5
1:8
1:10

NOTE: Higher gain stages also amplify any undesired noise component, which may be inherent in parts of the input signal.

Use the OFFSET parameter to shift the signal input level up or down. Can be used to match the readings obtained with an external meter, gauge or sensor.

The SCALE parameter can be used to amplify or compress an input signal level. It can be either positive or negative.

This is handy when there is a need to invert a signal, or when a larger input signal must be compressed or a small input signal needs to be scaled up.

Where the gain stages only offered fixed positive ratios, the SCALE parameter can be set to any arbitrary value.

Similar to the OFFSET parameter, adding or subtracting a certain BIAS amount from the input allows for shifting the result up or down after the SCALE operation.

As the BIAS is independent of the GAIN or SCALE, the output can be fine tuned with greater accuracy than with the OFFSET alone.

The QUANTIZER ensures that the output adheres to a specified step size.

For example, to guarantee that a temperature reading will be output with a step size of 1/8th of a degree, enter .125

To force, for example, a percentage value to a step size of 10, enter 10. Or specify zero to disable the QUANTIZER altogether.

Use the UPPER LIMIT to ensure that the adjusted analog value never exceeds the selected maximum. Set to +60Vdc by default.

Use the LOWER LIMIT to ensure that the adjusted analog value never dips below the selected minimum. Set to -60Vdc by default.

The OUTPUT FORMAT parameter takes a template string to make sure the readings obtained will be formatted according to the user specified requirements.

Use it to force the addition of the sign, or specify the number of digits to output. Drop the decimals. Add thousand separators. Allows outputting the final result with the desired level of precision.

A user defined UNIT STRING may be added after the final value is output to specify the desired unit.

Examples:

  • Vdc,
  • %,
  • m/s,
  • gal/h
  • mA

and many more.

INPUT PROCESSING

Calculations are performed in the following order:

      1. The input signal is routed through the GAIN stage, magnifying it by the chosen ratio or passing unaltered (1:1).
      2. The result value is read, filtered and averaged.
      3. The OFFSET value is added to/subtracted.
      4. The input is then up-scaled or down-scaled according to the configured SCALE.
      5. The selected BIAS will be applied.
      6. The result is run though the QUANTIZER to ensure the proper step-size is adhered to.
      7. The value is limited to the allowed range (must fit between the UPPER and LOWER LIMIT).
      8. The result is formatted according to the OUTPUT FORMAT.
      9. The UNIT STRING is added to produce the final result.

EXAMPLE

Convert an analog voltage in the range of 0 to 5 V to a percentage (0 to 100%), with 0 V representing 100% and 5 V representing 0%. To accomplish this, program the analog input as follows:

RESULT

Applying the above listed parameters results in the following, formatted output:

xR3_ai_example_b

SUMMARY

The flexibility offered by the NEXUS nano and RIO xR3 analog inputs processing stages allow even complex operations to be carried out on an input signal without the usual need for custom coding or scripting.

The relatively small input signal was routed through the 5x GAIN stage, resulting in a better coverage of the analog input range available (-60Vdc to +60Vdc). Next, the OFFSET and SCALE worked in combination to invert and properly proportion the signal. No BIAS was required, so the parameter was set to zero. The QUANTIZER ensured that the step size of 10 was strictly enforced. The UPPER and LOWER LIMIT parameters guaranteed that even while the input signal swung below or above the expected signal range, the output did not stray beyond the user specified boundaries. The OUTPUT FORMAT ensured that the output was properly formatted. Last but not least, the UNIT STRING allows for the proper interpretation of the result.

The example above clearly highlights the power of the available parametric interface. The web-based Optima GUI makes even complex operations easy.

OUTLOOK

The upcoming 2nd installment in this series will examine the next steps in the chain. It will showcase how to go from a raw input to defining multiple thresholds to generating escalating alarm notifications. Stay tuned.

Ralf Doewich

Optima Tele.com, Inc.

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