Accelerometer works on IPhone but not IPad...help?

Question

Hi everyone . iam trying to shake device with Accelerometer (NOT SHAKE API) because i have a problem with shake api . but idon't know why my code doesn't work on iPad !!! :

viewDidLoad:

[[UIAccelerometer sharedAccelerometer] setUpdateInterval:(1.0 / 40)];
[[UIAccelerometer sharedAccelerometer] setDelegate:self];

As a method :

- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {
    const float violence = 1.5;
    static BOOL beenhere;
    BOOL shake = FALSE;

    if (beenhere) return;
    beenhere = TRUE;
    if (acceleration.x > violence * 1.5 || acceleration.x < (-1.5* violence))
        shake = TRUE;
    if (acceleration.y > violence * 2 || acceleration.y < (-2 * violence))
        shake = TRUE;
    if (acceleration.z > violence * 3 || acceleration.z < (-3 * violence))
        shake = TRUE;
    if (shake) {
        // YOUR CODE HERE ****
    } 
    beenhere = FALSE;
}

thank you for any help ;)