Electrogoniometers

Motion Lab Systems is pleased to offer a comprehensive range of Goniometers and Torsiometers manufactured by Biometrics Ltd., in the United Kingdom. Formerly known as Penny and Giles, this company has a long history of providing quality products for the Biomechanics industry. Their goniometers are ideal for quick, simple, and accurate measurement of joint movement in multiple planes. Extremely robust, lightweight and flexible, the sensors can be comfortably worn undetected under clothing, without hindering the actual movement of the joint.

The sensors have been designed to be as light as possible and the operating force to be a minimum. This permits free movement of the joint without external influence.

Descriptions

The SG series twin axis goniometers permit the simultaneous measurement of angles in two planes, e.g. wrist flexion/extension and radial/ulnar deviation. Rotation of one endblock relative to the other about axis X-X is measured using one channel while rotation of one endblock relative to the other about axis Y-Y is measured using the second channel. Assuming the goniometer is mounted correctly, the outputs of the two channels are independent of linear displacements along axis ZZ. It should be noted that rotation of one endblock relative to the other around axis Z-Z cannot be measured. All twin axis SG series goniometers function the same way, the only difference being the physical size of the goniometer.

The F35 gomiometer permits the measurement of angles in one plane. Angles are measured when rotating one endblock relative to the other about axis X-X. The F35 goniometer is not designed to measure rotations about Y-Y. Any attempt to bend the unit in this way more than ± 20° from the neutral position will result in a reduction of the life of the unit. The goniometer does not measure rotations about axis Z-Z though this movement is permitted without reduced life occurring. This goniometer is designed for the measurement of finger and toe flexion/extension and is the smallest goniometer is designed to measure flexion/extension of finger and toe joints.

The Q series single axis torsiometers permit the measurement of rotations in one plane, e.g. forearm pronation/supination. Axial rotation of one endblock relative to the other along axis Z-Z is measured from the single output channel. If the torsiometer is bent in planes X-X or Y-Y the output remains constant. All torsiometers function in the same way, the difference being physical size.

The working mechanism is the same for all three types of sensor. Between the two endblocks inside the protective spring there is a composite wire that has a series of strain gauges mounted around the circumference. As the angle between the two ends changes the change in strain along the length of the wire is measured and this is equated to angle. The design is such that only angular displacements are measured. If the two ends move linear relative to each other, within the limits of the sliding endblock, without changing the relative angles between them, then the outputs remain constant.

In general, there are no fixed rules governing which size of sensor is most suitable for a particular joint; this depends on the size of the subject. The sensor must be capable of reaching across the joint so that the two end blocks can be mounted where the minimum movement occurs between the skin and the underlying skeletal structure. In certain circumstances more than one size of sensor will be appropriate. The following table is given for guidance only and refers to an adult population. Size used will vary within pediatrics.

Joint under investigation
Recomended Goniometer
Output measurement
wrist
SG65
flexion/extension, radial/ulnar deviation
Wrist (large)
SG75
flexion/extension, radial/ulnar deviation
forearm
Q150
pronation/supination
elbow
SG110
flexion/extension
ankle
SG110 or SG110A
dorsiflexion/plantarflexion, inversion/eversion
knee
SG150
flexion/extension
hip
SG150
flexion/extension, abduction/adduction
back
SG150B
flexion/extension/lateral flexion
neck
SG110
flexion/extension, lateral flexion
neck
Q110
axial rotation
finger
F35
flexion/extension
Operation

The working mechanism of the Biometrics Goniometers is the same for all three types. Between the two endblocks, inside the protective spring, there is a composite wire that has a series of strain gauges mounted around the circumference. As the angle between the two endblocks changes the change in strain along the length of the wire is measured and this is equated to angle. The design is such that only angular displacements are measured. If the two endblocks move in a linear path, relative to each other, within the limits of the sliding endblock, without changing the relative angles between them, then the outputs remain constant. The amount of strain induced in the gauges is inversely proportional to the bend radius that the beam is bent around. If the stated minimum permissible bend radius is exceeded then the life will be reduced or in severe cases failure may result.

WHEN USING ALL GONIOMETERS AND TORSIOMETERS THE MINIMUM PERMISSIBLE VALUE OF BEND RADIUS MUST BE OBSERVED AT ALL TIMES, PARTICULARLY WHEN ATTACHING AND REMOVING THE SENSORS FROM THE SUBJECT. FAILURE TO DO THIS WILL RESULT IN REDUCED LIFE.

Type
SG65
SG75
SG110
SG110/A
SG150
SG150B
Q110
Q150
F35
Channels
2
2
2
2
2
2
1
1
1
A max (mm)
65
75
110
110
150
150
110
150
35
A min (mm)
25
30
75
75
130
70
75
130
30
B (mm)
55
60
60
60
70
132
60
70
18
C (mm)
18
18
18
18
18
18
18
18
8
D (mm)
54
54
54
18
54
54
54
54
15
E (mm)
20
20
20
54
20
20
20
20
8
Weight (gm)
15
15
17
20
19
25
17
19
8
Goniometer Specifications

Typical lifetime for a Biometrics gomiometer is 600,000 cycles with an accuracy of ± 2 degrees measured over a range of ± 90 degrees. The repeatability of measurement is 1 degree measured over a range of 90 degrees. The operating temperature range is +10ºC to +40ºC with a temperature zero drift of no more than 0.15 degrees angle per degree C. Life test results have been collected by cycling the sensors through movements that would happen during everyday use. For example, placing a sensor on an adult elbow and moving from the neutral position to maximum flexion and back to the neutral position, the unit will function for typically 600,000 cycles.

Specification of crosstalk for all Biometrics twin axis SG series goniometers is less than ± 5% measured over an angular range of ± 60° i.e. if a joint is moved through 60° from the neutral position in one plane without movement in the orthogonal plane, then the sensor output in the orthogonal plane may change by a maximum of ± 3°.

The amount of strain induced in the gauges is inversely proportional to the bend radius that the beam is bent around. If the stated minimum permissible bend radius is exceeded then the life will be reduced or in severe cases failure may result.

GIB Goniometer Amplifier

The Goniometer Interface Box (GIB) is designed and manufactured by Motion Lab Systems. The GIB can power and amplify both channels of a twin axis (SG) Biometrics goniometers or two single channel (Q or F35) gomiometers and is designed to support Biometrics Goniometers with our EMG systems. Please read the Biometrics Goniometer User Manual before attempting to connect a goniometer to the GIB device.

Requiring only a minimum of power, the GIB not only powers the goniometer but also amplifies the signal to produce an adjustable signal output in the range of tens of millivolts per degree of flexion (instead of the normal ten microvolts per degree) allowing the user to interface any Biometrics goniometer directly to an analog to digital convertor (ADC) or any other measuring device such as a digital voltmeter, oscilloscope or an MA-300 EMG system that supports research channels.

The GIB has three BINDER style connectors - two of these connect directly to the Biometrics goniometer, while the third cable connects to any suitable power supply and provides two output signals. The GIB can be used with either two single axis goniometers, or a single twin axis goniometer. The two goniometer connectors are interchangeable (4-pin sockets) while the output connector is a single 5-pin connector, ensuring positive error-free connections. Extension cables (SGQ-002) are availabe (36" long, one per goniometer channel) that allow the GIB to be mounted at a distance from the goniometer(s) if required.

It is very important to note that the Goniometer Interface Box DOES NOT PROVIDE ANY ELECTRICAL ISOLATION between the goniometer and connections to the battery or signal monitoring system. If the Goniometer Interface Box is used with humans, it is strongly recommended that the system is connected to either battery operated equipment or used with a system that provides full electrical isolation for the subject such as a Motion Lab Systems MA-300 system or similar. The following GIB configurations are available:

  • GIB-000 - 5-pin BINDER with 60" cable terminated with solder tipped ends.
  • GIB-001 - Dual 5-pin BINDER with 60" cable terminated with 6-pin HARWIN (MA-300-xx-001)
  • GIB-002 - 5-pin BINDER with 60" cable terminated with 4-pin BINDER (MA-300-xx-002).
  • GIB-003 - 5-pin BINDER with 60" cable terminated with 4-pin LEMO.(MA-300-xx-003).
GIB Power Requirements and Output Signal

The GIB device requires 5 milliamps when supplied with +5 volt DC power and can operate from any unregulated DC power supply in the range of 4 to 9 volts. Each goniometer axis will add 6 milliamp to the GIB device requirements so a GIB with a twin axis goniometer will draw a total of 17 milliamps. Each GIB includes independent, regulated, power supplies for each goniometer axis.

The GIB device output is in the range of ±2 volts over a flexion range of +180º to −180º although the exact output voltage is subject to the characteristic of the goniometer and will vary from one goniometer to another. The GIB provides EXCITATION, GAIN and ZERO adjustment potentiometers for each channel.