Gravity meter S-99

1. Power supply test

The power supply has three testpoints, phase A, B and C. These are the gyro spin motor excitation voltages. The motor is 3-phase AC, driven by 200 Hz sinusoids, 120º phase shifted.

The phase voltages can be measured in two ways, a) Neutral (0V) to Line, or b) Line to Line.

1.1 Phase voltage

1.1.1 Using multimeter.

Meter setup: AC. Measure between 0V and each phase, and between phases. Also measure frequency, if the multimeter has this capability.

Test Point	Voltage	Frequency
	8.1 ± 0.3 Vrms	200 Hz ± TBD
	8.1 ± 0.3 Vrms	200 Hz ± TBD
	8.1 ± 0.3 Vrms	200 Hz ± TBD
-	14.1 ± 0.2 Vrms
-	14.1 ± 0.2 Vrms
-	14.1 ± 0.2 Vrms

TBD = To be determined.

1.1.2 Using oscilloscope.

Measure between 0V and each phase.

Note: Do not measure between phases by attaching the probe's ground clip to one of the phases - you risk making a short circuit if the scope's ground is tied to power supply 0 V. Instead make a differential measurement using two probes, ground clips to 0V, and then subtract ch.2 from ch.1.

The figure on the right shows phase A and B. Peak-to-peak value is approx 24 V. The phase difference can be measured to (1.7ms/5ms)*360º = 122º; the cursor readout is however not very accurate, so this just indicates the 120º phase shift.

Data from Tektronic oscilloscope TDS210. Calculated by Tektronix's WaveStar software.

2. Platform control unit tests

The testpoints are located on a small printed circuit board inside the Platform Control Unit, below the metal lid - see the figure to the right.. Learn the "nomenclature" - it makes testing easier:

X = Cross
L = Long
G = Gyro
A = Accelerometer
T = Torque
M = Motor

Note that "torque" applies to two components: a) The motors that keep the platform level, and b) the gyros, where the torque input signal is used to compensate for long-term horizontal reference changes (e.g. earth rotation). If you're not aware of this it can be a bit confusing.

Program switches SPRING TENSION and ALARM set to OFF.