Pauses the correct amount of time according to this 
        acquisition object's interval setting, and the last time this 
        function was called

def interval_wait(self):
        """Pauses the correct amount of time according to this 
        acquisition object's interval setting, and the last time this 
        function was called"""
        # calculate time since last interation and wait to acheive desired interval
        now = time.time()
        elapsed = (now - self.last_tick)*1000
        # print("interval %d, time from start %d \n" % (elapsed, (now - self.start_time)*1000))
        if elapsed < self.interval:
            # print('sleep ', (self.interval-elapsed))
            # self.signals.warning.emit('') # clear previous warning
            time.sleep((self.interval-elapsed)/1000)
            now = time.time()
        elif elapsed > self.interval:
            pass
            # self.signals.warning.emit("WARNING: PROVIDED INTERVAL EXCEEDED, ELAPSED TIME %d" % (elapsed))
        self.last_tick = now