Whenever I take data from the MCP3008, my sample rate keeps changing. Sometimes it’s 24ksps, sometimes 200sps. I want to keep this fixed. Python Code for SPI communication on raspberry pi:

import time
import sys
import spidev

spi = spidev.SpiDev()
spi.open(0,0)
spi.max_speed_hz=(3600000)

def readadc(adcnum):
    if ((adcnum > 7) or (adcnum < 0)):
        return -1
    r = spi.xfer2([1, (8+adcnum) <<4, 0])
    adcout = ((r[1]&3) << 8) +r[2]
    return adcout
ch0 = 0
seconds = time.time()

while (time.time() < seconds+1):
            pc_value = readadc(ch0)
            print pc_value
            output_file.write("%s \n" %(pc_value))

Thanks for your help!