A pulse graph is a visual representation of the duration of electrical activity measured on a TASER 7 CEW during a firing event.
Note: Pulse graphs in evidence generated before June 23, 2020 use an older pulse graph version. See the Legacy TASER 7 Pulse Graphs article for information on reading these types of pulse graphs.
Pulse graphs are uploaded to Axon Evidence.com and can be accessed from the appropriate Evidence Detail page by clicking View Graph, as shown in the example Evidence Detail page below.
The Pulse Graphs available on Axon Evidence are generated from the pulse data recorded in the TASER 7 CEW’s memory and contain electrical data about every pulse the CEW generates. This data includes the arc voltage, stimulation (stim) voltage, and output charge.
Voltage is the measure of potential for electric current to flow, and is measured in ‘volts’. When there is voltage in a connected circuit, electric current will flow. The amount of current that flows will depend on the electrical resistance of the circuit.
Resistance (also called “impedance”) is a measure of how much a circuit will resist allowing current to flow. If there is a lot of resistance (or high impedance) in the circuit, there will be a smaller amount of current. If there is a low amount of resistance (or low impedance), the there will be a larger amount of current.
Charge is the amount of electric current that flows over a period of time, measured in microcoulombs (µC). One (1) Coulomb is equal to 1 ampere of current over 1 second, therefore 1 microcoulomb is equal to 0.000001 amperes in 1 second (or 1 ampere in 0.000001 seconds).
The objective for the CEW is to generate a specific amount of current over time (charge), therefore the voltage is adjusted based on the resistance of the load the CEW discharges into.
TASER 7 Electricity Basics:
The arc voltage is the voltage across the arc capacitors (which are in charge of creating the electrical arc) in the TASER 7 CEW’s high voltage module. This voltage gives an indication of what level the capacitors needed to be in order to produce an electrical arc.
The stim voltage is the voltage across the stimulation capacitor (which delivers the energy to stimulate muscles) in the TASER 7 CEW’s high voltage module. The stim voltage indicates the voltage that the stimulation capacitor charged up to when an electrical pulse was generated.
The output charge is the amount of charge that was delivered in the pulse.
Why is this important?
The output charge and the arc and stim voltages give an indication of the load impedance (high or low) the TASER 7 attempted to discharge to and whether the load was stable or not.
- High Impedance Load: The load impedance can be high when cartridge probes partially connect and arc through skin and fat, drive-stun applications to skin and fat, or with probes contacting a subject with high adipose fat tissue content in that area. With this type of load, you may see low charge levels and high voltage levels.
- Low Impedance Load: The load impedance can be low when arcing across the cartridge bay, discharging into low resistance flesh, or discharging into another conductive material like salt water or metal. With this type of load, you may see optimum charge levels and lower voltage levels.
Using the pulse data within the pulse graphs, it is possible to determine whether the TASER 7 discharged into a low or high impedance, or even if there was no connection and it could not discharge.
Note: It cannot be determined if a deployment was effective or whether there was neuromuscular incapacitation (NMI) as a result by the pulse graph data alone. Pulse graphs are just a piece of the forensic puzzle.
Example 1 - Function Test:
This is an example of a pre-shift function test (Arc button). The TASER 7 pulses are arcing on Paths 1 and 2 from the CEW’s electrodes across the sides of the cartridges. In an open air arc, the high voltage ionizes the air and makes it a low resistance, so an open air arc is a low impedance. Therefore, we see the Stim voltage drop from the initial 2400 volts to approximately 1700 volts, and the charge stabilize near 63 uC. Due to the nature of open air arcing, the charge in this example varies between 56 and 68 uC.
Example 2 - Bay 1 Deployed, Both Probes Hit, Good Connection:
In this example, Bay 1 was deployed on a single trigger pull. Both probes contacted the subject and penetrated into the flesh. Since flesh is less conductive than an open air arc, we see the charge initially start lower than our target 63 uC, so the voltage in increased on each pulse until the charge levels at 62 to 63 uC, then the voltage is maintained at approximately 3100 to 3200 volts. Since the TASER 7 is conducting into the same load every pulse, the charge is stable and varies much less than an open air arc.
Example 3 - Bay 1 Hit, Bay 2 Hit:
In this example, there are 2 deployments. Bay 1 was deployed on the first trigger activation and made good contact, but close proximity to the subject had a short spread. Bay 2 was deployed and both probes made good contact. The graph indicates all 4 paths discharged at 11 PPS each (44 PPS total) and had stable charge at 60 to 63 uC. The Stim voltage was high, approximately 3300 to 3500 volts, indicating the load was a high impedance due to the non-conductive adipose fat in the are the probes hit.