# Calculating a correction factor

1. Jun 21, 2006

### laminatedevildoll

I am trying to calibrate this circuit, and it is hooked up to a voltmeter and also a power supply. When the circuit is horizontal, the voltmeter is supposed to read zero both in the x and y direction. Here, the x-direction is determined by tilting the circuit up and down and the y-direction is determined by tilting the circuit left and right (or something like that). Anyway, when I put the circuit on the leveled surface however, the voltmeter doesn't read zero for both x and y values. Therefore, in order for the voltage reading to read zero, I have sort of adjust the length of the four sides of the circuit so that the voltage is zero when it is on a leveled surface.

The circuit came with a calibration curve fit equation
theta = a + bV +cV**2+dV**3+eV**4+fV**5

where V is the X or Y output

and a,b,c,d,e,f is given for both the x-axis and the y-axis.

I calculated the angles using the voltage values I found when the circuit was leveled on the surface.

The voltage when the circuit is horizontal is 0.1999 arc degrees for the x-axis and -1.023 arc degrees for the y-axis. Using these values, I have to determine a correction factor for the four sides of the circuit, so I can make four stands to make the voltage zero when it's on a leveled surface. I'd appreciate if someone could give me some input on how I should do this. I know I have to use the angles I calculated somehow.

Last edited: Jun 21, 2006
2. Jun 21, 2006

### Staff: Mentor

Woof. What in the world are you talking about devildoll? Voltage does not have units of arc-degrees for starters. What is the device you are trying to calibrate? It sounds like it is some kind of tilt meter sensor?

3. Jun 21, 2006

### laminatedevildoll

Oops sorry. I meant the calculated theta (angle) from the equation above equals 0.1999 arc degrees for the x-axis and -1.023 arc degrees for y-axis. The measured voltages were 0.026 V for the x-axis and the -0.243 V for y-axis. I suppose the the value for the x-axis is close to zero, but the value for the y-axis is way off. So, I have to build four little stands of appropriate length so that when the device is on a leveled surface, the voltage reads zero. Yeah, I suppose you could say it's a title meter sensor, and it is going to be on a magnetometer.

Last edited: Jun 21, 2006
4. Jun 22, 2006

### Staff: Mentor

Not knowing exactly what the setup is, it's hard for me to make much of a suggestion. Can you just tilt the thing by hand until you get zero, and measure that angle? It sounds like you are wanting to make an adapter pre-tilt thing to get zero out when the adapter+sensor are placed on a level surface, so just tilt the sensor until you get zero, and make something that provides that tilt. Better yet, squish the sensor down in some soft putty on a level surface and tilt it to get zero, then let the putty dry into a permanent adapter.

5. Jun 22, 2006

### laminatedevildoll

Yeah, I guess when I tilt the tiltmeter, I can get a zero voltage for both x and y. However, in order to make something that makes the tilt, my advisor wants me to calculate by how much for each side. So, since I have the x and y angles (calculated from the calibration curve fit equation which came with the device), and the length of each side, I guess I could use trig, maybe, the tan function to calculate the required height to make the correction right?

By the way, here's a link of the device

http://www.geosystems.com.au/pdpm02.html

Last edited: Jun 22, 2006
6. Jun 22, 2006

### Staff: Mentor

Sounds right. Looks like a fun project!