DSP2

DSP2 Specifications

This product is discontinued. Information is for reference purposes.

The DSP2 is a four channel board which accepts as inputs the output of one or more installed channels. The user selects the waveforms to be used as inputs. The input waveforms must be currently broadcast over the internal bus and are usually supplied by other peripheral boards such as AWP1 and AWP2. Input waveform can also be output waveforms generated by the DSP board itself. By using this feature, a user can perform multiple sequential processing. The output waveforms appear to the system as if they were from an analog signal conditioner such as the AWP1. They can be recorded, captured and sent to an external monitor for monitoring (with appropriate options installed). The DSP2 is considered a 4 channel waveform source and a system may have multiple DSP2s.

Supported Functions are:

  1. X+Y (addition)
  2. X-Y (subtraction)
  3. X*Y (multiplication)
  4. X/Y (division)
  5. SQ(X) (X squared)
  6. SQRT(X) (square root of X)
  7. FREQ(X) (rate meter, cycles per second)
  8. RPM(X) (rate meter, revolutions per minute)
  9. INT(X) (integration)
  10. D/DT(X) (differentiation)
  11. AVG(X) (average)
  12. COPY(X) (duplicate)
  13. NV(X) (inversion)

Where X and Y are any installed channel

Operation Summary

Arithmetic Operation: X+Y, X-Y, X*Y, X/Y, SQ, SQRT
Independent input waveform(s) are combined to create an output waveform. Each input and the output can be independently scaled by 1/100, 1/10, 1/2, 1, 2 or 10. Input is always considered to be a % of full scale, but the user selects the reference as center or edge. If edge is selected, the input range is 0 on the right grid edge and 100 on the left. If center is selected the range is -50 to +50.

Integration (INT(X))
Integration is often referred to as 'area under the curve' where the output waveform is generated by continually adding up the area under the input curve. A constant input results in a ramp when integrated - the ramp begins to rise when the input is non-zero and levels off when the input returns to zero. This example is used to illustrate that integration devices are sensitive to offsets. Any offset will cause the output to rise continuously until it is off the chart.
To minimize this effect the input waveform should be adjusted so that it is on the reference point (usually the center) when the input is zero. To further eliminate drift, reset features are provided to force the output back to zero. These are:

  1. Manual reset
  2. Reset when the input goes through zero
  3. Reset when the output reaches a user defined level.

In addition, the DSP2 provides an optional high pass filter which will eliminate small offsets before they affect the integration process (DCBLOCK). The time constant (TC) also has an effect on the integration process. The term derives from the traditional analog integrator and for most purposes can be considered an output scale factor. As the time constant is increased, the output is attenuated. In the previous discussion it was stated that the output (integration) of a non-zero constant is a ramp. For the same input, the ramp would rise more slowly as the time constant was increased. The integrator time constant can have values from 1 to 1000 milliseconds. The rectification feature allows the user to alter the input waveform before it gets to the integrator.
Choices for rectification are:

  • None Normal Operation
  • Positive Integrate only the positive portions of the input waveform
  • Negative Integrate only the negative portions of the input waveform
  • Full Convert negative waveform values to positive before integrating

Differentiation (d/dT)
The output of a differentiator equals the rate of change of the input waveform. Other terms for this are slope and slew rate. Because the process of differentiation acts to amplify noise, it must be limited in bandwidth. The DSP2 differentiator is not useful for signal above 100 Hz.

Like integration, there is a time constant associated with differentiation. It also acts as an output scale factor but, in this case, the gain will appear greater as the time constant increases. Be aware that at high time constant values, you will see noise even when the input is grounded. This is because even random changes of a single bit will be seen as large rates of change.

Rate Meter (FREQ(X), RPM(X))
The DSP2 provides two types of rate meter functions. Both types detect the frequency of a single input waveform by measuring the time between level crossings. In order to optimize the result, the user is given the ability to adjust both amplitude hysteresis and a minimum time between counts (dead space). The RPM (revolutions per minute) function has a maximum range of 10,000 RPM while the FREQ (cycles per second) has a maximum range of 1000 Hz.

Average (AVG(X))
An input waveform is processed to create an output waveform by performing a 'moving window average'. The user selects the size of the window by specifying the number of points (taps) to be averaged for each output point. Up to 100 taps can be used. The resulting output waveform can be scaled by 1/100, 1/10, 1/2, 1, 2, or 10. The choices for sample rates are: 100, 200, 500, 1000, 2000, 5000, 10000 and 20000 Hz.

Copy (COPY(X) and Invert (INV(X))
The COPY function allows the user to record a scaled copy of the input channel in another location. The INV function allows the user to record an inverted and scaled version of the input channel in another location. The invert function can be referenced either to grid center or grid edge.

Copy and invert are useful when implementing multiple stage equations where the output from one DSP2 channel is used as the input to another.

Other Considerations
Aliasing - Aliasing, a distortion of a sampled waveform, occurs when an input waveform contains frequencies which are more than 1/2 the sample rate. The K2 contains an 20 kHz anti-aliasing filter. This is not sufficient to prevent aliasing when the DSP2 is used - it will be up to the user to make sure the input signal bandwidth is limited.

Polarity - the polarity of the waveform is particularly significant for some DSP2 operations so the zero point of the input waveform must be clearly established by the user.

Specifications subject to change without notice