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15 Sensoray Model 417

Chapter 4 Programming

Set Filter

This command establishes a software single-pole low-pass filter for the specified channel. The

second command byte specifies unsigned filter factor, F, which may have any value from 0 to 255,

inclusive. The relationship between F and filter percentage, P, is:

All channel filter factors default to zero after a reset. This effectively disables the filters and maxi-

mizes channel response. A non-zero factor in electrically noisy environments may help to reduce

measurement noise.

Rather than computing the theoretical value of filter constants, we recommend that you experi-

ment with different values to find the best response/noise tradeoff. Some applications, however,

require knowledge of the filter time constant. This expression describes the relationship between

time constant t, expressed in seconds, and filter factor F:

COMMAND: (160 + Chan), (FilterFactor)

RESPONSE: NONE

VB Code Example:

‘*********************************************************************

‘ Generic procedure to set filter factor on any channel.

‘*********************************************************************

Sub SetFilter(BasePort%, Channel%, FiltFactor%)

Const SET_FILT = 160 ‘ SET FILTER CONSTANT command opcode

‘ Send command string to coprocessor board

Call SendByte(BasePort, SET_FILT + Channel)

Call SendByte(BasePort, FiltFactor)

End Sub

‘*********************************************************************

‘ Set up channel 4 with a 12.5% low-pass filter. To convert filter

‘ percentage (0 to 100%) to filter factor, multiply by 2.55.

‘*********************************************************************

Call SetFilter(BaseAdrs, 4, 12.5 * 2.55)

FInt2.55

P×()

NumActiveChannels–

45ln

256

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