KSR SERIES INSTRUMENTS
Measure Moment of Inertia and Center of Gravity with Unprecedented Accuracy!

Model KSR17000 - Measures MOI and
CG of objects weighing up to 17,000 lbs

Product Documentation

Product Sheets:   KSR Series (Imperial Units) (1.3 MB)   KSR Series (Metric Units) (1.3 MB) Specifications:   KSR Series (Imperial Units) (29 KB)   KSR Series (Metric Units) (32 KB)

Technical Papers

A New High Accuracy Instrument For Measuring CG and MOI

PRODUCT OVERVIEW

Space Electronics KSR series instruments continue to offer the highest accuracy available for CG and MOI measurement. These combined instruments are available in a variety of sizes and measure two coordinates of center of gravity and one moment of inertia in one setup.

TYPICAL APPLICATIONS

KSR series are used primarily by the defense and space industries to measure high end payloads such as:
    • Spacecrafts
    • Spacecraft subassemblies
    • Bombs, missiles, and torpedoes
    • Military components
    • Aircraft engines

They have also been used by various other industries to measure payloads such as:
    • Car engines
    • Transmission components

HIGHLIGHTED BENEFITS

Highest Accuracy - Space Electronics KSR series instruments offer the highest accuracy available for CG measurement with the use of closed-loop force rebalance technology.  Since their development more than 20 years ago, our KSR systems have proven to be superior to conventional passive technology (such as load cells). 

Dynamic Range - Our KSR instruments have a dynamic range that is greater than 30,000 to 1.  One instrument can cover a range of payload weight previously requiring two machines! 

New Concept - The KSR concept improves all of the performance criteria of the previous KGR series:  sensitivity, dynamic range, linearity, stiffness, and overload protection.  Dynamic range and sensitivity are increased by a factor of 100.  Linearity and stiffness are improved by a factor of 5.   Finally, the new design has an overload capability at least 3 times as great as conventional technology.

Center of Gravity measurement along two horizontal axes in a single setup with better than +/-0.001 inch (0.025mm) accuracy for payloads weighing as little as 4% of machine capacity!

Moment of Inertia measurement around a vertical axis with accuracy better than +/- 0.1%.

Fully Automated Operation - Select CG or MOI on the computer, and the entire measurement takes place automatically.  There is no need to manually rotate the table or clamp the torsion rod.

Test Reports can be printed as each test is completed (can be customized for your particular application). All data is saved in a database for later retrieval or reprint.

Unbalance Moment is measured directly.  Corrections can be made with the test part mounted and changes in CG observed immediately.

Fixturing Errors Are Minimized by dial indicating the test part on the rotary table.

Correction Weights and locations computed to achieve test part static balance.

Active moment transducer - KSR Series instruments exhibit Performance that is 10 to 100 times better than any previous designs.  This improvement is the result of a new technology:  an active closed-loop transducer.   When an overturning moment due to the test object CG offset tries to tilt the axis, the optical sensor detects a deflection and an equal and opposite torque is applied to the measuring system to hold the measurement axis vertical.  Since high loop gain is used, the system is rigid and has fast response.  Unbalance moment is determined by measuring the torque motor current required to restore the system to a level condition.

Gas bearing - The extraordinary dynamic range and accuracy of the moment transducer would be wasted if conventional bearings were used as a pivot.   This instrument uses a gas bearing to support the weight of the payload.  The friction in this bearing is 1000 times less than conventional bearings.  The runout is less than 0.03mm.  Since the bearing rides on a film of air molecules, it has absolutely no wear.  Twenty years later this bearing will be as accurate as a new bearing.

Automatic elimination of leveling errors - Conventional center of gravity instruments will give erroneous answers if the mounting table is not perfectly leveled.  This effect is particularly noticeable when measuring tall objects.   On our machine, the payload is mounted on a rotary table which is programmed to stop at 0°, 90°, 180° and 270°.  CG offset moments are measured at each position.   This data allows computation of CG coordinate locations along two horizontal axes.   Averaging of CG offset moments displaced by 180° eliminates leveling and zero shift errors.

Effect of Payload Weight - Since the weight of the payload is totally supported by the gas bearing and none of this force is applied to the torsion rod, the instrument is insensitive to payload weight and may be calibrated using a single test mass.  The moment of inertia indication will then be linear over the full range of weight and moment of inertia specified for the instrument.

Computer included - A computer is supplied with each instrument.  A series of menus allow the operator to select the desired procedure for calibration, measurement, or calculation.  Prompts on the screen guide the operator through each procedure so that the operator rarely needs to refer to the instruction manual.

Software Options - The computer can be programmed to calculate the mass properties about axes other than the rotational axis of the machine.  Custom report formats are available.  Optional custom software calculates the correction weights required to balance a specific object.  Optional interface and software permits communication with another computer.

Easy Moment of Inertia Measurement - By selecting to measure MOI, the lower end of the torsion rod is automatically clamped to create an inverted torsion pendulum, and oscillation is initiated by an air cylinder.  In this mode, the payload oscillates in a rotational sense about a vertical axis through the center of the instrument's rotary table.  The period of oscillation is measured with the fixturing alone (tare period T_°), then with payload mounted (T_x).  MOI is then computed using the formula: I = C(T_x²-T₀²) where C is the calibration constant.

High Speed KSR - A high speed model of our KSR is available. Operation is three times faster, with the same level of accuracy as standard models. More...

More details on KSR instruments:
    • Instrument Design Details
    • Selecting Instrument Size
    • L Adapter fixture for horizontal payload orientation