VHF Eartag Transmitter

Current Telonics VHF transmitters use either the MK-11 or MK-12 electronics. Sensor options available with these transmitters are described below grouped by primary use: mortality, activity, and temperature monitoring. There is some overlap between sensor types and how they are used, with typical uses as described. If you have questions about sensors or how they might best be implemented in your study please call Telonics to discuss your application.

Changes in motion or temperature are detected by unit's sensors and result in changes in the units transmitted pulse period. Pulse period is the time between the start of one transmitted pulse and the start of the next transmitted pulse, and it is measured in milliseconds (ms). Pulse rate in beats per minute (bpm) = pulse period/60,000.

With inclusion of the Data Logging Option, sensor data can also be stored-on-board the transmitter and downloaded using Telonics Data Converter (TDC) at the end of the study if the transmitter can be recovered.

Both the MS6 mortality-motion option and the MA activity option use an on-board accelerometer as the sensor to detect changes in position and acceleration in three axes. The sensor is sampled and each second is classified as active or not depending on whether a change in position or acceleration has been detected in that second.

The MS4 temperature option and MS5 temperature-triggered mortality option are based on an on-board thermistor used to measure temperature.

The MS6 mortality option can be enabled in conjunction with the MA activity sensor or MS4 temperature sensor. In such cases the activity or temperature sensor will be used to determine the active/alive pulse period.

Other sensors cannot simultaneously be used to control the transmitted pulse period, but if the Data Logging Option is purchased, multiple sensing options (e.g. MA activity and MS4 temperature) can be purchased and their resultant data stored-on-board the transmitter.

Mortality Sensing Options:

Mortality - Motion sensor (MS6)

This option provides active/alive and inactive/mortality pulse periods. Depending on the length of time over which activity is evaluated (time-out interval), this sensor can be thought of as either a mortality sensor (e.g. timeout interval of 4-12 hours) or as a motion sensor (e.g. with a timeout interval of seconds to minutes). Typically it is used as a mortality sensor, which is the most common sensor option used.

Users specify the following:

1. Time-out interval over which the active versus inactive evaluation is made,
2. Minimum number of active seconds to keep the transmitter in the active pulse rate (5 seconds is the default),
3. Active pulse rate or period,
4. Inactive pulse rate or period.

For example, if the time-out was defined as 6 hours, the default 5 active seconds was used, active pulse period was 1000ms (60 bpm), and inactive pulse period was 600ms (100 bpm); then as long as there were at least 5 active seconds in the preceding 6 hours, the pulse rate would be 60 bpm. If 6 hours elapsed with fewer than 5 active seconds the pulse rate would shift to 100 bpm. If ≥ 5 active seconds were again detected within any 6 hour window (e.g. if a scavenger moves the transmitter), the pulse rate would immediately switch back to 60 bpm.

When used as a mortality sensor, the active pulse rate is typically set to a comfortable tracking rate (often ~50-60 bpm), and the inactive/mortality pulse rate is faster. This helps conserve battery life because the active rate will be common, and the inactive rate rare. Users may alternatively select a slower inactive rate; for example, such programming is commonly used on bears which hibernate and are inactive for long periods of time.

If this sensor is used with short time-out intervals (e.g. minutes rather than hours), it serves as a motion sensor, rather than a mortality sensor. Operation is as noted above, but the inactive mode would be triggered much more frequently than with long time-outs. Such short time-outs are uncommonly used, but with an example application being to help determine the effect of disturbances on resting animals by having the inactive rate triggered after a few minutes of inactivity, but with the active rate immediately triggered if the animal is startled and begins moving.

When the MS6 option is activated, date and time of the most recent 9-16 changes from active to inactive or back are stored by the transmitter. This data can be downloaded using Telonics Product Programmer (TPP).

The MS6 option can alternatively be selected to provide information on how long it has been since the animal died or became inactive by having the inactive/mortality pulse periods related to how long the transmitter has been in that mode. If ordering the option with this feature, four additional values are specified:

1. Maximum elapsed time of concern after mortality is detected (up to 1000 days),
2. Pulse period that corresponds to the specific time when mortality is detected,
3. Pulse period that corresponds to the maximum time of concern after mortality is detected,
4. Whether a simple linear scale or a segmented scale of 2-8 pieces is used. A linear scale provides constant resolution over the defined range of pulse periods. A segmented scale allows finer resolution of elapsed time immediately after mortality is detected and coarser resolution later on. Each segment has resolution that is twice as coarse as the segment before it. Telonics provides a graph and linear equations to convert an observed pulse period into an elapsed time.

Temperature-Triggered Mortality option (MS5)

This option is designed to change pulse period/rate when measured temperature drops below a user-specified value. If temperatures rise back above the defined value, pulse period will change back to the default/higher temperature period. A typical use would be to detect mortality in an implantable transmitter in an endothermic animal, where temperature rather than motion could be a better indicator of mortality. For example, it has been used in waterfowl where waves could prevent a motion-based mortality sensor from detecting mortality. Another use of this option has been in vaginal implants to determine parturition, where the temperature would drop and the pulse period change when the unit was expelled. This option might not be suitable in areas where a high ambient temperature prevents the transmitter from cooling after death or parturition.

Users specify the following:

1. trigger point temperature
2. pulse period above the trigger point temperature
3. pulse period below the trigger point temperature

With this option, an alternative is to have a range of pulse periods determined by how long it has been since the animal died (temperature dropped below the defined threshold). This operates as described above for the MS6 sensor.

Activity Sensing Options:

Activity Sensor (MA)

This option adjusts pulse period based on the amount of activity within a user-defined interval. The pulse period can either be defined as one of two periods (active versus inactive) or scaled over a range of pulse periods. Changes in pulse period step through time; e.g. the amount of activity in interval 1 determines the pulse period in interval 2, activity in interval 2 determines pulse period in interval 3, and so on. Thus, the pulse period being transmitted always reflects the amount of activity in the prior activity data collection interval. This is illustrated in tabular form below.

Active/Inactive mode: In each defined interval, one of two pulse periods is transmitted depending on the amount of activity in the proceeding interval.

Users specify the following:

1. Classification interval (1-second default, but selectable between 1-255 seconds)
2. Active pulse period,
3. Inactive pulse period,
4. Time interval over which data is evaluated (up to 100 minutes)
5. Number of active classification intervals (typically seconds) required for the time interval to be considered active. If any activity is detected during the defined classification interval that interval is considered active.

For example, the classification interval could be defined as 1-second, active pulse period 1000ms (60 bpm), inactive pulse period 1500ms (45 bpm), the time for accumulation of data as 1-minute, and the number of active seconds required to designate as active as 10 seconds. In this case the VHF would operate at either 45 or 60 bpm depending on whether the number of active seconds was <10 or ≥10 in the prior 1-minute accumulation period.

Scaled pulse period mode: In each defined interval, pulse period is scaled within a user-defined range based on the amount of activity in the preceding interval.

Users specify the following:

1. Classification interval (1-second default, but selectable between 1-255 seconds),
2. Range of pulse periods to be used for scaling,
3. Time interval (1 second up to 18 hours) over which activity is evaluated.

For example, the classification interval could again be 1-second, data could be summed over a 10-minute time interval, and the range of possible pulse periods could be 1000-3000. In such case, pulse periods would vary between 1000 and 3000ms (60-20 bpm) depending on the amount of activity in the prior 10-minute accumulation period. Increased levels of activity would result in shorter pulse periods.

With this option the user can also select whether the relationship between activity and period is linear or a segmented scale (with 2-8 segments). A linear scale provides a constant resolution between the number of active classification intervals and pulse period over the specified range. Segmented scales provide different resolution for each segment, with the first segment (starting at 0 activity counts) having the best resolution, and each following segment with resolution that is twice as coarse as the segment before it. Telonics provides a graph and linear equations to convert an observed pulse period into a number of "active classification intervals" over the update period.

Mortality - Motion Sensor Option (MS6)

If this sensor is used with short time-out intervals (e.g. minutes rather than hours), it serves as a motion sensor, rather than a mortality sensor. Operation is as noted in the more detailed description under Mortality Sensing Options above, but the inactive mode would be triggered much more frequently than with long time-outs. An example of such use is to help determine the effect of disturbances on resting animals by having the inactive rate triggered after a few minutes of inactivity, but with the active rate immediately triggered if the animal is startled and begins moving.

Temperature Sensor (MS4)

This option measures temperature at a defined sampling interval and causes pulse period to change with changes in temperature. Telonics provides a graph and linear equation to convert an observed pulse period into a temperature. Temperature sensing transmitters have uncalibrated accuracy shown in the table below. If higher accuracy is desired, the user can calibrate individual units.

Users specify the following:

1. Sampling interval (1 second to 18 hours),
2. Low-end temperature of concern with a corresponding pulse period,
3. High-end temperature of concern with a corresponding pulse period.

Option 400 is the standard version of this sensor. It has a thermistor mounted on the electronics board (thus measuring internal package temperature, which may differ from either ambient or body temperature), and is centered at 37°C.

Option 401, is similar to Option 400, but the thermistor is centered at 14°C.

If you have a need for an externally mounted thermistor, please contact Telonics to discuss your application.

Sensor details:

Calibration, if desired, is the responsibility of the user, consisting of a 1-point calibration at the listed temperature.