Calibration

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Calibration

CALIBRATION

Even though the CES is shipped after being fully calibrated it is recommended that the calibration of the CES be checked after installation. Calibration is a crucial function to ensure the accuracy of all data. The CES maintains calibrated values under normal use conditions.

There are three separate phases to Calibration which allow the user to ensure the accuracy of all data generated by the CES. These three phases allow for Hardware Diagnostics, Calibration, and Calibration Checks. Each of these phases allow for testing, measurement and, if necessary, adjustment of CES instrumentation. The calibration mode allows for proper adjustment of the system for accurate measurement and maintenance support. The same method of menu driven screens used with other modes of the CES will guide the user through the calibration and diagnostic procedure.

The Ariel System menu offers a series of selections; Exercise, Program, Calibrate, Data Analysis and Report Gen. Type "C" or use the cursor to highlight Calibrate and then press "Enter" to begin calibration. The next screen is the Calibration Main Menu. The first thing that should be done is Hardware Diagnostics. Press F2 to call up the Utility Menu screen.

9.1 Hardware Diagnostics

Hardware Diagnostics are an important first step in the performance of calibration, because it performs a check on the accuracy of the electronic range of the hardware. The accuracy of all the other data needed for a full calibration of the system cannot be guaranteed until this phase in the Calibration is complete. The Utility Menu will display three options. After Hardware Diagnostics are complete, pressing END will return the user to the the Calibration Main Menu.

9.1.1 Valve

Perform a stepper motor test to step the valve throughout its range and see if it travels all the way from locking the bar on one hand to totally releasing the resistance on the other. To test for proper functioning of the motor select Valve, press ENTER. After the Valve Position Screen appears follow these steps:

Type "400", press ENTER. The bar should be locked in both directions.
Type "0", press ENTER. The bar should be released.
Find what will be the smallest value that you can enter for valve position and the bar will remain locked. (Normal range should be between 205 to 400).
Type "0", press ENTER to reset the valve to home position. Type the value that was found for bar locked to assure consistency and to verify your findings.

9.1.2 AD Values

The AD_Values monitors digital voltage information. This information is provided from the pressure transducer, in units of force, and the angular potentiometer in units that measure the position of the bar. The values for these two measurements are given in numeric form. The first value reports the average pressure (force) from a sampling rate of 16,000 samples per second. This value should be approximately 3500 500 units. The second value is the RMS (Root Mean Square) which represents the amount of change or variation form the average value.

The average value for position reports the position of the bar relative to its lowest and highest ends of the range of motion. The range for the average value should be no less than -4090 to no more than +4090. This change should be sequential and linear throughout the range from low to high position and high to low.

The first step in Hardware Diagnostic is to test the AD_Values in order to ascertain proper connection between the computer and the transducers mounted on the hydraulic pack in the exercise machine, and second, if the system is operated within the correct voltage limits.

9.2 Station Parameters

Station Parameter is used to set the following information about the exercise station. It is also used to select system options such as measurements.

	Station ID: You may enter the name of you facility.
	Station Type: indicates whether the Multifunction or the Arm-Leg station is being used.
	Units selects the units of measurements, English or Metric.
	Bar Measure selects how the bar position is measured and reported. Linear reports the movements in linear units, for example, inches or centimeters. Angular reports movement in degrees around the pivot point. We recommend Angular bar measure, especially for the Arm-Leg or Back station.
	Bar Length is a measurement from the axis of rotation of the bar to the handle on which the calibration weight will be placed. the bar length for the Arm-Leg should be set to 14 inches and the bar length for the Multifunction should be set at 56 inches. These values are given by the manufacturer.

The next three items on the screen relate to the hydraulic valve.

	Valve Open is normally set for minimal resistance when moving the bar. The Valve Open position is always 200 steps less than the Valve Lock position.
	Valve Lock is the minimum number of steps the valve has to travel in order to lock the bar from any position.
	Valve Range refers to the total number of steps in the full range of movement of the hydraulic valve in the stepper motors. The Valve range shouldn't be changed. Normally the Valve Range should be 75-100 steps greater than the Valve Locked position.
	Bar Range is the full range of movement of the bar from the lowest to highest position. The actual values of these parameters will never change, as they are mechanically fixed.
	Ouch Limit is the feature that protects the exercise station from damage if excessive force is applied to the bar. In the event that the force on the bar exceeds the value for which the system is calibrated (whichever is lower), the Ariel CES will open the valve and terminate the exercise in progress.
	Response selects how rapidly the hydraulic valve will respond to an application of force on the bar. There are five settings: Slowest, Slower, Medium, Faster, and Fastest. Slowest will give the best "feel" during normal exercise. If exercise will be performed at low force levels a higher speed will achieve the optimum response. Faster or Fastest, for normal exercises, may result in the valve opening too quickly during the exercise.
	Step Rate is the rate at which the motor runs through it's range. This is set by the manufacturer and should not be changed.

9.3 Position Calibration

This option sets a relationship between the full travel of the bar and the values measured from the position transducer in the exercise station. A series of screens will instruct you to move the bar first to its lower limit and then to the upper limit. Follow the directions on the screen to perform the necessary calibration.

	Use a level or an angle Finder for measuring angles.
	Make sure that the bar is positioned exactly as requested and that it is not moving.
	Then press any key on the keyboard and the system will measure that bar position.
	When this step is complete, you will return to the Calibration Menu, or if you are running a Full Calibration, you will return to the next calibration procedure below.

9.4 Valve Calibration

This procedure sets the stepper motor step positions for the usable range of the hydraulic valve (see Station Parameters). A series of screens will instruct you to move the bar to a high position (for the Arm-Leg-Back, about 15-20 degrees forward of vertical upward). You'll be asked to hang weights on the bar (50 pound suggested) and then signal by pressing a key. The Ariel CES will then automatically determine the valve limits. The system will then report and store those limits in station parameters and instruct you to move the weights.

	For Valve Calibration, as well as the following two procedures, be sure to stand away from the bar as it moves, to avoid contact with the falling weights.
	Advance either to the Calibration Menu, or to the next procedure described below.

9.5 Torque/Force Calibration

Force calibration sets a correspondence between the force on the handles of the bar and the values measured from the pressure transducer on the hydraulic resistive mechanism o the exercise station.

	The user will be asked to enter two weight values to be used in calibration: the first should be low, 35-65 pounds, and second should be higher, 100-200 pounds or more. If no certified weights are available this calibration should not be run. We recommend the use of round barbell weights after you have careful and accurately determined the exact weight utilizing a professional quality weight scale.
	First the screen will display instructions to move the bar to the lowest position and press any key. The next screen will display a warning requesting you to move the bar very slowly to the highest position possible. While you move the bar up slowly the computer collects readings of pressure throughout the range of the bar. The readings are organized in a calibration table which is used to determine the values for zero force measurements throughout the bar range. Fast movement will cause higher pressure in the system and will affect the accuracy of the force calibration. Press a key when the bar is highest.
	The next screen will ask you to move the bar first to the stop and then the start position, in this way, the system determines the portion of the range of motion that is being calibrated, as well as the bar direction (up or down). Since the weights must fall during calibration, make sure the stop position is low and the star position is high.
	The bar will lock at the the Start Position and you will be asked to hang the amount of weight on the bar which was specified for trial No. 1. Once the correct weight is hung on the bar, you may press any key. The machine will then automatically release the bar slowly and the weights will be dropped through the range of motion. After the bar stops the system will tell you to remove the weight. The system takes 16,000 measurements per second of the weight in every bar position.
	The system will then instruct you to go back to the start position and will tell you to hang the amount of weight specified for the second trial. The same procedure as above will then be repeated. You will then be asked to remove the weight.
	The screen will return to the Force/Torque screen to allow you perform calibration for the Up direction if you wish.
	To do this, repeat the above steps with a calibration bar. To exit, press the End key. System calibration is stored and saved.
	To perform an Up calibration, you must have the optional calibration bar. The Up calibration procedure is identical to the Down calibration procedure. Since most facilities won't have this, you must select "YES" on the Calibration Menu in order to exercise the option to compute the Up calibration from the Down calibration.

9.6 System Accuracy

The analog measurement of transducer values on the Ariel systems have an accuracy limitation by the finite representation in a digital computer. Because data values must change by one bit (binary digit) hen represented digitally, any give transducer measurement could have a possible error approaching one bit-value.

In practical terms, the absolute accuracy depends on the resolution of the conversion from analog values to digital values. On the Ariel CES, one bit-value typically represents 0.3 pounds of force, and about 0.01 of one degree of bar movement.

These accuracy levels are entirely sufficient for the vast majority of resistive training and rehabilitation uses. It is possible to adjust the system for greater level of accuracy.

9.7 Calibration Check

This F1-Calibration Check item on the Calibration Main Menu checks or verifies the current system Force Calibration. You will be asked to move the bar to the stop and Start positions. The bar will lock, and you will then be asked to hang a known weight on the bar.

	Press any key and the bar will slowly fall through the range of motion.
	The system will then plot a graph of measured Average Force vs. Position on the monitor. The average value over the range tested will also be displayed.
	You may copy this graph on your printer by pressing the "Cntrl" and PrtSc" keys for a copy of system calibration.

9.8 Abort Calibration

This feature permits you to erase or discard any calibration changes you made during this session. Press Esc key from the Calibration Main Menu to abort and you will return to the Ariel system menu display screen.

This feature is handy when you are learning about calibration, as it lets you experiment with the calibration options without changing the system calibration.

You will also be shown the current maximum force or torque that your exercise station can measure, based on your calibration.

If these figures are not reasonable, i.e. force is less than several hundred pound, than calibration was not done correctly, or you console A/D board is not properly adjusted.

If recalibration does not correct the problem, have your system checked by a qualified technician.

9.9 Measurement Limits and Resolution Limits

Each exercise station has separate transducers which are separately calibrated:

Pressure Transducer for calibrating force.

Angular Potentiometer for calibrating Position and Velocity.The force and position transducers have adjustable ranges (gain and offset adjustments) so the maximum forces can be set electronically to measure either higher or lower values than the current set up limits. These adjustments should only be done by an authorized Ariel technician,

The current maximum force limit that can be measured are always displayed at the top of the calibration menu screen. They are labeled "Max_Torque" or "Max_Force".

9.10 Resolution

The approximate resolution for the pressure transducer is a 13 bit (1/4096), and for the Angular Potentiometer the resolution is up to 14 bit (approximately 1/8192). These resolution values represent a fixed percent of the value as given below:

	Force = 0.0244%
	Position = 0.0122%

For Multi-Function systems with a maximum force set for 1200 pounds, a bar range of 65 degrees, and a maximum speed set for 200 degrees second, the approximate resolution is:

	Force = 0.293 pounds
	Position =0.008 degrees

As you can see, the CES offers a wide range of force and velocity measurements, and at the same time the system maintains very high resolution, providing the clinician with high precision measurements. Thus, the same exercise systems can be used for precision diagnostics in rehabilitation applications, and on the other hand as a "heavy duty" training device utilized by elite athletes.

9.11 System Checkouts

To insure that your system performs accurately, it is important to periodically check you force and position calibration If the calibration differs significantly from the actual measured values, the appropriate calibration procedure should be performed. Your systems should also be recalibrated if the hydraulic resistor pack is changed in the exercise station, or if the analog interface board is changed in the console. The validity and the accuracy of the system is the responsibility of the operator or clinician. Ariel Headquarters will provide any support needed in the performance of a Calibration check.

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