Sandberg Serrell Automated Balance Calibration Machine

NASA Ames has a Sandberg Serrell Automated Balance Calibration Machine which can apply multiple combined loads on a wind tunnel balance. The lab's current inventory of machine-to-balance adapters can accommodate 2.5 to 4.0 inch TASK balances. The machine is a unique tool in wind tunnel balance calibration technology. It can generate simultaneous combinations of three forces and three moments within its load envelope. Without the physical limitations of dead weight manual loading, the Automated Balance Calibration Machine can be used to bring calibration load schedules closer to real tunnel load conditions, thus increasing the accuracy of the calibration. Load schedules are prepared from Excel spreadsheets. The machine specifications are shown below.

Machine Specifications

Maximum Balance Size
Diameter		8in (20cm)
Length		30in (76cm)
Machine Load Capacities
Normal Force		10,000 lb	(44000 N)
Side Force		5000 lb	(22000 N)
Axial Force		1500 lb	(6600 N)
Pitch Moment		40,000 in*lb	(4500 N*m)
Yaw Moment		20,000 in*lb	(2250 N*m)
Roll Moment		30,000 in*lb	(3400 N*m)
Load Condition Tolerance
Normal Force		2 lb	(8.8 N)
Side Force		1 lb	(4.4 N)
Axial Force		0.5 lb	(2.200 N)
Pitch Moment		5 in*lb	(0.56 N*m)
Yaw Moment		5 in*lb	(0.56 N*m)
Roll Moment		5 in*lb	(0.56 N*m)
Load Cell Type		Interface® Ultra Precision
Load Cell Accuracy		0.03% of Full Scale (preloaded)
Balance Reposition Tolerance
Angular		0.001deg (4 arc seconds)
XYZ		0.0001 in
Balance Position Sensor Resolution		0.00002 in	(0.00005cm)
Linear Actuator Resolution		800,000 Encoder Steps per inch
Calibration Data Acquisition Rate		1 minute per Load Point

Facility

The lab is located in a temperature controlled high bay room, with dimensions of 40x60x20h.

Calibrated Weights

The lab has an versatile inventory of weights, ranging from 1 lbs. to 1000 lbs. The weights are calibrated to 0.03% of quoted value.

Data Acquisition Instrumentation and Compution Analysis

The lab uses HP Instrument Controllers, PCs and Macs for data acquisition, analysis and database storage. The Data Acquisition and Control Systems can provide accurate, flexible, multi-channel, and continuous acquisition of voltage, current, resistance, and temperature. The systems also have real-time balance monitoring to ensure a balance is always operating under design limits.

Data reduction of strain gage balance calibrations uses analysis software packages developed at Ames Research Center. Bal Cal lab performs calibration analysis using industry-wide accepted load iteration procedures (AIAA Recommended Practice R-091-2003) in combination with a recently developed automatic math model selection algorithm. Calibration software also performs load envelope analysis of strain-gage balance data.

This analysis software package computes a data reduction matrix for a given balance calibration data set. During a wind tunnel test this data reduction matrix is used in combination with a load iteration scheme in order to compute loads from measured electrical responses.

Force Transducers

The lab also uses calibrated uni-axial load cells with 0.03% full-scale accuracy, with cells varying in range from 1000 to 10000 lbs.

Balance Support Rigs

There are two sting support rigs that can accommodate taper mounted balances from 0.75 to 4.0 inches.

Loading and Balance Hardware

The lab maintains an inventory of roll arms, calibration bodies, axial loading plates, flexures, knife edges, and weight pans for many balance sizes. Also maintained are a number of dummy balance gages and master taper gages.

Position and Angle Sensors

To generate an accurate calibration, both the applied load and its vector must be known accurately. To insure that applied loads are positioned accurately, we enlist an variety of devices depending on the situation. The devices include: 2-axis quartz-flexure (inertial navigation) accelerometer levels with 0.0001 degree resolution, bubble levels with 3 arc second resolution, optical transits with a 2 arc second level line of sight reference and optical grade mirrors and prisms.