AHRS400 Series User’s Manual
Doc# 7430-0004-01 Rev. A Page 17
Calculate the temperature with the following calibration:
T (°C) = 44.4 (°C/V) * (V
temp
(V) – 1.375 V)
The DMU temperature sensor is internal to the DMU, and is not intended to
measure the ambient temperature. The internal temperature of the DMU
may be as much as 15°C higher than the ambient temperature.
3.9 Analog Output
The AHRS400 Series of products provide nine fully conditioned analog
outputs; of these, six are output voltages created by a DAC in the DMU.
The analog signals can be connected directly to an ADC or other data
acquisition device without further buffering. The input impedance of any
data acquisition device should be greater than 10 kΩ for the DAC outputs
and relatively higher impedance for raw analog outputs. The circuit diagram
for the raw accelerometer outputs (Pin 5, 6 and 7) is shown below:
The DMU must be set to scaled sensor measurement mode or angle
measurement mode to enable the analog signals.
The analog outputs from the accelerometers are taken directly from the
sensor through a buffer. They are “raw” in the sense that they do not
represent a calculated or calibrated value. You will need the zero bias point
and scale factor given on the DMU calibration sheet to turn the analog
voltage into an acceleration measurement.
To find the acceleration in G’s, use the following conversion:
accel (G) = (V
out
(V) – bias (V))*sensitivity (G/V)
where accel is the actual acceleration measured, V
out
is the voltage at the
analog output, bias is the zero-G bias voltage, and sensitivity is the scale
factor in units G/volts. This applies only to the signals on pins 5, 6, and 7.
For example, if the x-axis of your accelerometer has a zero-G bias of 2.512
V, a sensitivity of 1.01 G/V, and you measure 2.632 V at the analog output,
the actual acceleration is (2.632 V – 2.512 V)*1.01 G/V = 0.121 G.
The analog outputs for the angular rate signals are not taken directly from
the rate sensors; they are created by a D/A converter internal to the DMU.
The output range is ± 4.096V with 12-bit resolution. The analog data will
represent the actual measured quantities, in engineering units, not the actual
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