Legacy and PhysioTel HD Implants

The DEM and MX2 derive activity using the same method; however, Ponemah v5.x and v6.x differ in available Derived Parameter options. Please remember, Activity is a relative measurement used to answer the question: “Is the animal moving (active) or not (inactive)?”

When using PhysioTel and PhysioTel HD implants, Activity counts are not directly generated by the implant, but instead are generated by the Data Exchange Matrix (DEM) or the Matrix 2.0 (MX2). As the Subject moves about in its cage, the telemetry signal transmitted to the receiver antennas varies in strength. The signal strength may vary due to orientation of the animal relative to the receiver, or due to the distance of the animal from the receiver antennas. When the signal strength changes by a certain amount, the DEM/MX2 generates an Activity count. The number of counts generated is dependent on both distance and speed of movement.

 The actual number generated depends on the following factors:

• Transmitter model.
• Speed with which the transmitter moves.
• Any outside interference such as a nearby transmitter or power source.
• Slight variation from receiver to receiver.

Therefore, comparing the Activity count output of implants against each other only makes sense relatively – is the animal moving or not. Since the Activity waveform is in counts, the accumulated counts over the logging period, normalized to a minute, is of most value to obtain. The following outline the recommended Derived Parameter to select for the Activity waveform given the Ponemah version being used and the type of the matrix (DEM or MX2).

DEM with Open ART in Ponemah 5.x

• Reports Activity in counts per minute, updated every second, regardless of sample rate
• The activity input channel will change in steps of 60 since a difference of 1 count in a second translates to 60 counts/minute
• When reporting activity, A_Mean should be used to get a result in counts/minute

MX2 with Ponemah 5.x

• Reports activity in counts per sampling interval and counts are reset at the end of each sampling interval
• Sampling the activity channel at 1Hz will yield counts per second, sampling at 10Hz will yield counts per decisecond
• The activity channel on the MX2 should not be sampled at a rate higher than 10Hz, doing so results in a distorted activity signal that cannot be averaged correctly.
• When reporting activity A_Mean should be used to get a result in counts/sampling interval
• It is recommended to sample Activity at the default sampling rate of 1Hz in order to get Activity reported  in counts/sec.
• When it is desired to report Activity in Counts/min , A_Mean   should be multiplied by a factor of 60. In Ponemah versions higher that 5.4, a custom derived parameter can be created for this calculation.

MX2 with Ponemah 6.x (v.6.2 and later)

• Reports activity in counts per sampling interval and counts are reset at the end of each sampling interval
• Sampling the activity channel at 1Hz will yield counts per second, sampling at 10Hz will yield counts per decisecond
• The activity channel on the MX2 should not be sampled at a rate higher than 10Hz, doing so results in a distorted activity signal that cannot be averaged correctly.
• It is recommended to sample Activity at the default sampling rate of 1Hz in order to get the Activity signal reported  in counts/sec.
• For reporting Activity in counts/min, the parameters Total Activity (A_TA) and Total Activity 2 (A_TA2) should be used.

• Total Activity (A_TA) reports the integral of the Activity signal over a 60 second duration. When sampling the Activity channel using the default sampling rate of 1Hz the A_TA will equal the sum of the Activity values over the 60 seconds. This results in values with units of counts/minute.
• Total Activity 2 (A_TA2) reports the integral of the Activity signal over the defined Logging Rate, normalized to a minute. When sampling the Activity channel using the default sampling rate of 1Hz the A_TA2 will equal the sum of the Activity values over the Logging Rate. This results in values with units of counts/minute.
• Note: Since Ponemah reports derived data based on the Logging Rate, Total Activity 2 is the recommended parameter for use with Activity for Ponemah v6.20 and later. 

Ponemah v6.00-v6.12 reported Activity differently, as the default sampling rate was 10 Hz and the default Activity Reset value was 1. These defaults would also cause inconsistencies with accumulating the activity counts when using Scheduled Sampling. Ponemah v6.20 corrected the default sampling rate (1 Hz) and Activity Reset (60) values, as well as added ATA2 parameter for more accurate, consistent reporting. If you collected Activity data using Ponemah v6.00-v6.12, please see the following article for details on how to normalize the values to the expected Counts/min:

How to normalize to Ponemah Activity Parameter to Counts/min.

PhysioTel Digital Implants

PhysioTel Digital implants contain a three-axis accelerometer used by the Ponemah software to report activity measurements. The three-axis accelerometer provides acceleration data along the x-, y-, and z-axes, relative to the orientation of the implant. Acceleration for the x-, y- and z-axes is reported as a value from an analog-to-digital converter. A range of at least -7Gs to +7Gs is provided, with a corresponding output from approximately 0 to 4095. A value near 2047 will be displayed when zero acceleration for a given axis is sensed-- when in a steady, neutral alignment (orthogonal) to earth’s gravitational field. The displayed sampling rate for the x, y and z axis acceleration data is 10Hz.

Along with the values from each axis of the accelerometer, Ponemah will also report an Activity value calculated from the accelerometer axes in Jerks. The accelerometer Jerk calculation is as follows:

Where C is a constant based on the delta time for the accelerometer sampling rate.

C = Sampling Rate * 3.5347

The default Sampling Rate for Activity channels is 1 Hz.

It is recommended to use Total Activity 2 (A_TA2) which reports the integral of the Activity signal over the defined Logging Rate, normalized to a minute. When sampling the Activity channel using the default sampling rate of 1 Hz, the A_TA1 will equal the sum of the Activity values over the Logging Rate reported in units of Jerks/minute.

Difference between implants with replacement accelerometer

The replacement accelerometer showed improvement in the x-,y-, z-axis signal noise providing a better signal to noise ratio.  This results in a lower baseline level of the calculated activity value.  There is no impact to the individual x-,y-, z-axis data regarding range or sensitivity.  Below are screenshots from static bench testing.

Original Accelerometer	Replacement Accelerometer