Hi Nathan
Thank you so much for replying. Thank you for your suggestion about the 10:1 ratio. Yes, I have access to all the text based examples provided with the CD and the ones online.
Here is the PID loop code
DAQmxCreateTask("",&taskHandle);
//Creating an angular displacement read channel using the counter (ctr0) with Ticks = 8384 and quadrature decoding
DAQmxCreateCIAngEncoderChan(taskHandle, MCP_fl_enc_A_chan,"",DAQmx_Val_X4,0,0.0,DAQmx_Val_AHighBHigh,DAQmx_Val_Degrees,Ticks,0.0,"");
//Specifying pin at which Encoder A is connected = source, with rate as 1000 samples/sec and 100 samples per channel.
DAQmxCfgSampClkTiming(taskHandle, MCP_fl_enc_A_port,1000.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,100);
//Activating Quadrature encoder read task
DAQmxStartTask(taskHandle);
//read once before loop starts (timeout = 0.001)
DAQmxReadCounterScalarF64(taskHandle,timeout,data,NULL);
//converting float64 to double
doubledata = double(data[0]);
curr_angle = (doubledata);
//calculate initial error and scale it down.
errorpid = (angle_deg-curr_angle)/720;
//Error tolerance set to 0.0001
while (abs(errorpid) > tol){
data[0] =0.0; // <========== Initializing the read data as 0 to check if data has stopped coming or just stopped updating
//proportional gain
P = Kp*errorpid;
//Derivative gain
D = (errorpid-prev_error)*Kd;
prev_error = errorpid;
//Accumulating error for Integral gain
acc_error = acc_error + prev_error;
I = acc_error*Ki;
//some random limits for avoiding integral overflow
if (I > 1) I=0.01;
if(I<-1) I= -0.01;
//calculating PWM out
PWM_out = (PWM_out + (P + I + D)) ;
//limiting PWM out
if (PWM_out > 5.0) PWM_out = 5.0;
if (PWM_out < 0) PWM_out = 0;
value = PWM_out;
//function to send an analog out ov value= value using AO 0
MoveMotor(MCP_fl_ctrl, value); // DAQmxErrChk (DAQmxCreateAOVoltageChan(motor_sig,channel,"",0,5,DAQmx_Val_Volts,""));
//stop Motor after the pulse
Stop_Motor(1);
prev_angle = curr_angle;
// read again
DAQmxReadCounterScalarF64(taskHandle,timeout,data,NULL);
doubledata = double(data[0]);
errorpid = (angle_deg-curr_angle)/720;
}
Sleep(100);
DAQmxStopTask(taskHandle);
DAQmxClearTask(taskHandle);
I haven't included the error checks at each function call in here to reduce the length a little. After your question , I added a data initialization at the beginning of the loop to see
if encoder data had just stopped updating or has completely stopped sending data. It seems, the data just stops because after a few reads, the output becomes 0 permanently.
The only angular read example is a continuous read which requires an external clock source which I currently dont have. So I modified the program a bit and converted the continuous
read to a scalar read with other parameters being the same (Rate = 1000 and samples 100). Now the read function is:
DAQmxErrChk (DAQmxReadCounterScalarF64(taskHandle,10.0,data,0));
Now after acquiring some data, it shows the error,
Multiple sample clock pulses were detected within one period of the input signal. Use a sample clock rate that is slower than the input signal. If you are using an external sample clock, ensure that clock signal is withing the jitter and voltage level specifications and without glitches.
Property: DAQmx_Read_RelativeTo
Requested Value: DAQmx_Val_CurrReadPos
Property: DAQmx_Read_Offset
Requested Value: 0
Status Code: -201314
So I figured that my sample rate is too high, I went all the way down to 10(can we go below 1?) to maintain the 10:1 ratio and all the way up to 1MS/s but it keeps popping the same error
at random times (some times it reads upto 70 degrees sometimes upto 2 degrees on the same settings.)
I can't figure out what is wrong because signal express just shows pristine results.
Thank you so much for your time and patience.
