Moog Crossbow VG700MB Series - Manual (Page 13)

VG700M User’s Manual
Doc.# 7430-0280-01 Rev. F Page 7
The VG700M serial interface connection is standard RS-422. Power is
applied to the DMU on pins 4 and 5. Pin 4 is ground; Pin 5 should have 16-
32 VDC unregulated at 0.5 A. If you are using the cable supplied with the
DMU, the power supply wires are broken out of the cable at the DB-9
connector. The red wire is connected to the power supply output; the black
wire is connected to the power supply ground. DO NOT REVERSE THE
POWER LEADS.
3.3 Interface
The VG700M has a standard RS-422 serial interface. The unit is
configured with a 38400 baud rate, 8 data bits, 1 start bit, 1 stop bit, no
parity, and no flow control.
3.4 Measurement Modes
The VG700M is designed to operate as a vertical gyro; however, you can
also use it as a six-axis sensor. The VG700M can be set to operate in one
of three modes: voltage mode, scaled sensor mode, or angle (VG) mode.
The measurement mode selects the information that is sent in the data
packet over the RS-422 interface. See “Data Packet Format” for the actual
structure of the data packet in each mode.
3.4.1 Voltage Mode
In voltage mode, the analog sensors are sampled and converted to digital
data with 1 mV resolution. The digital data represents the direct output of
the sensors. The data is 12-bit, unsigned. The value for each sensor is sent
as 2 bytes in the data packet over the serial interface. A single data packet
can be requested using a serial poll command or the DMU can be set to
continuously output data packets to the host.
The voltage data is scaled as:
voltage = data*(5 V)/2
12
,
where voltage is the voltage measured at the sensor, and data is the value
of the unsigned 16-bit integer in the data packet. Note that although the
data is sent as 16-bit integers, the data has a resolution of only 12 bits.
3.4.2 Scaled Sensor Mode
In scaled sensor mode, the analog sensors are sampled, converted to digital
data, temperature compensated, and scaled to engineering units. The digital
data represents the actual value of the quantities measured. A calibration
table for each sensor is stored in the DMU non-volatile memory. A single
data packet can be requested using a serial poll command or the DMU can
be set to continuously output data packets to the host. The data is sent as
signed 16-bit 2’s complement integers. In this mode, the DMU operates as
a six-axis measurement system.