1.5.12. Processing Plugins¶

1.5.12.1. Eval Plugin¶

This plugin evaluates an arithmetic expression and replaces the data sample(s) of its owner to with the result. This plugin is available for both parameters and channels, for the latter it executes at the time plugin stage of the data processing. It is activated by the following configuration line:

eval expression

The supported expression format is identical to the one described on the Computed Tab with one exception: In this context self referencing expressions (i.e. ones that contain the owner as an operand) are allowed.

1.5.12.2. FIR Filter Plugin¶

This plugin implements an FIR (Finite Impulse Response) digital filter. These filters execute at the raw plugin stage of the data processing. This module is activated by entering a line with one of the following two forms in the processing configuration:

firfilter Type Proto Order Fmin [Fmax [Tune]]
firfilter Type File

Where:

• Type: L, H, N, B.

  • L = Low pass
  • H = High pass
  • N = Notch
  • B = Band pass

• Proto: PM, HN, HM, NU, BL, BH, BN, GA.

  • PM = Parks-McClellan optimal filter design (recommended).
  • HN = DFT generated filter with Hanning Window.
  • HM = DFT generated filter with Hamming Window.
  • NU = DFT generated filter with Nuttall Window.
  • BL = DFT generated filter with Blackman Window.
  • BH = DFT generated filter with Blackman-Harris Window.
  • BN = DFT generated filter with Blackman-Nuttall Window.
  • GA = DFT generated filter with Gaussian Window.

• Order: Filter order (number of ‘taps’).

• Fmin: Filter frequency (Low end value for notch and band pass).

• Fmax: High end frequency value for notch and band pass.

• Tune: Tuning parameter for ‘PM’ filters.

• File: Filter coefficient file to use. See below.

Synthesized Filters

All frequency specifications are for the cutoff frequency (or 3dB point) of the filter. The built-in synthesizer will accept the 1..99% range of the channel’s Nyquist rate for the filter frequencies. The accepted order range is 5…253 for the FFT-based filters and 9..127 for the Parks-McClellan filter.

The optional tuning parameter for the Parks-McClellan filter has a practical range of 0.5..2.0. It can be used to adjust the width of the filter’s transition band. In general, a narrower transition band will mean more ripples and vice-versa. The default transition band size is determined based on the filter’s order, and results in approximately 0.1dB pass-band ripple.

Filters Created from Data Files

This module supports loading FIR filter coefficients from a custom APEX defined CSV file format. Several such files have been included with this distribution, consult any of them for the supported syntax.

• Filter types L and H require only one additional argument: The filter file name.
• Filter types N and B require two filter file name arguments: These are used to define the lower and upper frequencies of the resulting notch or band filter.

All included filter files are defined as low pass filters with inversion and concatenation taking place within the plugin as necessary for H, N and B filter types. All files contain zero phase filters meaning that there will be no phase shift as a function of frequency when using them.

The FIR filters listed below are provided in the install package of this APEX software. The pass band and stop band are listed as a percentage of the sample rate for the channel. Keep in mind that the pass and stop band values will swap whenever the filter is transformed for a high pass application.

1.5.12.3. IIR Filter Plugin¶

This plugin implements an IIR (Infinite Impulse Response) digital filter. This plugin is used at the time plugin stage of the processing. It is activated by entering a line with one of the following two forms in the processing configuration:

iirfilter Type Proto Order Fmin [Fmax [Ripple [Atten]]]
iirfilter File

Where:

• Type: L, H, N, B.

  • L = Low pass
  • H = High pass
  • N = Notch
  • B = Band pass

• Proto: BU, BE, CH, IC, EL.

  • BU = Butterworth Filter.
  • BE = Bessel Filter.
  • CH = Chebyshev Filter.
  • IC = Inverse Chebyshev Filter.
  • EL = Elliptical Filter.

• Order: Filter order (number of ‘poles’ and ‘zeros’).

• Fmin: Filter frequency (Low end value for notch and band pass).

• Fmax: High end frequency value for notch and band pass.

• Ripple: Pass band ripple in dB (0.01..6.0).

• Atten: Mimimum stop band attenuation in dB (30..120).

• File: Filter coefficient file to use. See below.

Synthesized Filters

All frequency specifications are for the cutoff frequency (or 3dB point) of the filter. The built-in synthesizer will accept the 0.05..99% range of the channel’s Nyquist rate for the filter frequencies. The accepted order range is 1..10. The Elliptical and both Chebyshev filter types can be tuned with the optional pass band ripple and stop band attenuation parameters. Defaults are 0.1dB for ripple and 60dB for attenuation. Generally, using more permissive values for these will result in a sharper transition band.

Filters Created from Data Files

This module supports loading IIR filter coefficients from a custom APEX defined file format. Several such files have been included with this distribution, consult any of them for the supported syntax. Matlab generated ‘FCF’ format files are also supported.

The included filter files are pre-generated low frequency high pass Butterworth filters mostly intended for removing low frequency noise (such as 50 or 60 Hz power, etc..) from measured channels. These filters are not invertable (unnlike the FIR filter files listed above). Their naming convention is:

IIR_H_BU_###_##.dat

Where the first group of three digits represents the cutoff frequency in 1/1000th-s of the sample rate. The second two digit group indicates the filter order (3, 6 or 10). Filters were generated for every 1/1000th increment in the cutoff frequency, but only the numerically stable ones are included in this software distribution.

1.5.12.4. Decibel Scaled Stats¶

This plugin generates dB scaled channel stats from the supported ‘standard’ APEX DS/DX ‘amplitude’ type stat values (RMS, peak to peak, zero to peak or average). This plugin executes at the peak plugin stage of the data processing. It is invoked via a formula line of the following form:

dbstat nominal stat min max alarm warning

The arguments and their default values (when omitted) to this plugin are as follows. Note that the last four values are optional.

• nominal: nominal signal level for 0 dB [in EU].
• stat: base stat name. accepted: RMS, P2P, PEAK and AVG
• min: plot axis minimum [dB] (default: -40)
• max: plot axis maximum [dB] (default: 40)
• alarm: alarm level [dB] (default: no alarm)
• warning: warning level [dB] (default: no warning)

This plugin applies to processed data only.

1.5.12.5. Windowed Stats Plugin¶

This plugin produces a copy of the ‘standard’ APEX DS/DX channel stats over a longer time window instead of the duration of a single block. The new statistics are available under signals in the plot data selector tree and can be used in the alarms window. This plugin executes at the time plugin stage of the data processing. It is activated by the following configuration line setup:

windowstats avgtime

Where:

avgtime: time interval in seconds over which the stats will be averaged. Specify time range from 0.01 to 10.00 seconds.

1.5.12.6. Order Track Plugin¶

This plugin adds channel stats tracking selected orders based on the value of the default forcing speed parameter assigned to the channel. This plugin executes the peak plugin stage of the data processing. It is invoked via a configuration line of the following form:

ordertrack orderspec …

One or more order specifications can be given. Each order specification has the following format:

ORDER/ORDERTOL/FREQTOL:ALARM:WARNING

Where:

• ORDER: The value [i.e. forcing parameter multiplier] of the order to track.
• ORDERTOL: Tolerance band in order units, Default is 0.1
• FREQTOL: Tolerance band in frequency units. Default is the channel FFT bin width.
• ALARM: The [red] alarm level. Default is no alarm.
• WARNING: The [yellow] warning level. Default is no warning.

1.5.12.7. Alarm Levels Plugin¶

This plugin does not do any processing on the data. Its only purpose is to add alarm limit values to already defined ‘standard’ channel statistics. This plugin is nominally assigned to the peak plugin stage of the data processing. It is invoked via a configuration line of the following form:

statlimit limitdef ...

One or more limit definitions can be given. Each limit definition has the following format:

STATNAME:ALARM:WARNING

Where:

• STATNAME: The name of the stat for which limits are defined.
• ALARM: The [red] alarm level.
• WARNING: The [yellow] warning level. This can be omitted.

1.5.12.8. Thermocouple Plugin¶

This plugin converts measured DC voltage data into a temperature value using standard thermocouple (type B, E, J, K, N, R, S, T) conversion tables available from NIST. Output can be scaled in different temperature units. This plugin executes at the time plugin stage of the data processing. It is activated by the following configuration line:

thermocouple TYPE CJC UNIT

Where:

• TYPE: thermocouple type (B, E, J, K, N, R, S, T)
• CJC: cold junction compensation
• UNIT: temperature units (K, C, F)

1.5.12.9. Spike Filter Plugin¶

The spike filter plugin implements an non-linear digital filter for removing short duration spikes from a channel’s raw input data. This plugin executes at the raw plugin stage of the data processing. It is activated by the following configuration line:

spikefilter CFL MAXN MAXW CSAT

Where:

• CFL: Crest Factor Limit, samples above this limit are considered noise. The crest factor is the ratio of a sample’s deviation from the data block’s mean value versus the data block’s RMS average. [Default = 4]
• MAXN: Maximum number of noise spikes the filter will remove from a data block. [Default = 4]
• MAXW: Maximum permitted width of a noise spike the filter will remove from a data block. [Default = 6]
• CSAT: When non-zero then re-check the data for saturation if it was flagged as saturated, and if this filter removed any spikes. [Default = 0]

If the input data block contains more spikes or wider spike(s) than the specified limits, the data is not modified at all. If the count and width(s) of the detected spikes are within the specified limits then all found spikes are removed via linear interpolation using samples on the sides of each spike.

This filter adds the number of spikes as a 1/block statistics value to the channel’s stats.

1.5.12.10. Spike Noise Plugin¶

This plugin is a companion to the spike filter plugin described above. It will flag peaks as noisy when spikes found by the spike filter could not be removed. If all spikes were removed or no spikes were found, the data will not be flagged as noise. This plugin executes at the peak plugin stage of the data processing. It is activated by the following configuration line:

noisespikes

This plugin has no arguments.