Quadrature
The Quadrature instruction is used to measure the output from an incremental encoder.
Syntax
Quadrature ( Dest, Port, Option, Mult )
Example
The following example program shows the use for the Quadrature instruction. It was written for a CR300 datalogger, but can be used in other dataloggers with slight changes to port number.
Public Quad(4), LevelFt
Alias Quad(1) = Accum
Alias Quad(2) = NetDir
Alias Quad(3) = CountsUp
Alias Quad(4) = CountsDown
'multiplier = wheel circumference / counts per rev
'1 ft circumference wheel; 100 counts per revolution
'multiplier = 1/100 = .01
Const Mult = 0.01
'Constant Table to Enter Observed Stage
ConstTable (Observation,0)
Const ObsLevelFt = 0
EndConstTable
BeginProg
LevelFt=ObsLevelFt
Scan (1,Sec,1,0)
Quadrature(Quad(1),C1,0,Mult)
If NetDir <> 0 Then
LevelFt = LevelFt + Accum
EndIf
NextScan
EndProg
Remarks
The Quadrature instruction is used with single ended type (A and B) quadrature encoders. A digital port pair is used to monitor the two control tracks of the encoder. The instruction calculates the displacement and direction of the encoder.
Parameters
Dest (Destination)
The variable array in which to store the results of the measurement. Dest must be dimensioned to four to hold the following values:
- Dest(1): Accumulator. Net number of counts from channel A and channel B. Count will increase if Channel A leads Channel B. Count will decrease if Channel B leads Channel A.
- Dest(2): Net direction. Indicates direction if a change occurs.
- 1 = A change in pulse count has occurred, where A is leading B since the last stop in pulse count.
- 0 = No change (default).
- -1 = A change in pulse count has occurred, where B is leading A since the last stop in pulse count.
- Dest(3): Number of counts in direction 1 (A leading B) that have occurred since the last time the instruction was executed.
- Dest(4): Number of counts in direction 2 (B leading A) that have occurred since the last time the instruction was executed.
Type: Variable Array
Port
Specifies which digital port pair to use for monitoring sensor channels A and B, respectively. Valid ports are:
| Code | Description |
|---|---|
| C1 | Control Ports 1 and 2 |
| C3 | Control Ports 3 and 4 |
| U1 | Universal Ports 1 and 2 |
| U3 | Universal Ports 3 and 4 |
| U5 | Universal Ports 5 and 6 |
| U7 | Universal Ports 7 and 8 |
| U9 | Universal Ports 9 and 10 |
| U11 | Universal Ports 11 and 12 |
Type: Constant
Option
Determines how each channel is counted.
| Code | Description |
|---|---|
| 0 | X1 - Counts will increase on rising edge of Channel A when Channel A leads Channel B. Counts will decrease on falling edge of Channel A when Channel B leads Channel A. |
| 1 | X2 - Counts will increase at each rising and falling edge of Channel A when Channel A leads Channel B. Counts will decrease at each rising and falling edge of Channel A when Channel A leads Channel B. |
| 2 | X4 - Counts will increase at each rising and falling edge of both channels when Channel A leads Channel B. Counts will decrease at each rising and falling edge of both channels when Channel B leads Channel A. |
Type: Constant
Mult (Multiplier)
Constant, variable, array, or expression by which to scale the results of the measurement.