FAQ - Tilt Sensor

194 - What causes the bias level in the tilt sensors to drift over time?

The bias level may drift for several reasons. The most important is that changes in temperature can cause the sensor bias level to drift. This translates into a change in angle output. The CXTILT02EC is temperature compensated to minimize this effect.

Also, a large shock can shift the bias level. Heavy vibration may also cause the sensor bias levels to shift.

321 - I'm having problems connecting the tilt sensor to my com port.

We test each sensor before we ship it, so the sensor interface should be working when you receive it. Check that you are connected to the correct com port; check that you are using the correct communications parameters (9600 baud, 8 data bits, 1 stop bit, no start bit, no parity and no flow control.) If you are using AccelView, the program will tell you if it can find the sensor on the specified com port.

397 - I collected the readouts from the sensor and tried to verify by using the formula in the Crossbow paper. But the number did not make sense. The formula: Tilt Angle = Inverse sine ((Vout-Zero Angle Voltage)/Sensitivity) Vout= 4.4 Volts, Zero Angle Voltage = 2.5 Volts, Sensitivity = 34.9 miliVolts or 0.0349 Volts Tilt Angle = Inverse sine ((4.4-2.5)/.0349) = Inverse sine (54.44) ? Did I miss something here?

In order to use the non-linear equation, you need to use the Sensitivity in V/G (NOT V/deg). You can convert the sensitivity provided in V/deg into V/G as follows:

V/G = (V/deg)/sin (1) = 0.039/0.0175 = 1.9997.

If you use this value in your equation now, you should get,

Tilt Angle = asin [(4.4-2.5)/1.997] = 71.82 deg.

424 - We are designing signal conditioning for various sensors and we need to know the output impedance. Your specification sheet identifies Output Loading. It looks the same output impedance although I've never see it expressed along with capacitance in nF. Is it the same thing?

Output loading resistance (Rl) normally refers to the minimum load you should have on the sensor output to avoid creating voltage devider. The output loading capacitance (Cl) is the maximum capacitance you can have on the sensor output. If your load capacitance exceeds the recommended value, you may not get the full bandwidth of the device.

On page 33 of the Application Data for Tilt Sensors there is a Pin Diagram for Pins 4,3,1 & 11. Pin 4 is designated as Transmit Data - Is this Transmit FROM the Tilt Sensor OR Transmit from the PC ? Pin 3 is designated as Receive Data - Is this Receive FROM the Tilt Sensor OR Receive from the PC ?

All our Pin configuration is with reference to the sensor (NOT PC). Hence,
Pin 4 - Transmit from CXTILT
Pin 3 - Receive to CXTILT

436 - How water resistant are your analog tilt sensors?

Our analog tilt sensors are hard potted and packaged within aluminum or plastic housings. This makes them water-resistant, although we haven't documented any specific weatherproof ratings for our accelerometers. But, we can say that these are splash-proof and can withstand dirt and water spray effectively for upto IP65. Since the the place where the cable enters the housing has only been padded, without an o-ring, it might not withstand if you try to hose-down with a spray. However, the electronics inside the housing are hard-potted are well-protected.

Memsic FAQ Tilt Sensor
Memsic FAQ Tilt Sensor