Dean Huster
Well-Known Member
There is absolutely no way in the world that you can measure the current in a circuit without affecting the circuit in some way. A resistor in series with the line inserts series resistance and voltage drop. A current probe, current transformer or current "clamp" introduces an inductance into the line. The design of any of these current measuring methods strives to minimize these effects by keeping the insertion resistance and/or inductance to as low a value as possible.
Tektronix has provided more methods of DC and AC current measurement that probably any other company. They have passive AC current probes (HF transformers in the heads) that are good from around 500 Hz to over 250MHz, depending upon the model. These probes also have fantastic pulse characteristics. They have DC/AC probes (Hall-effect sensors in the heads) that are good from DC to at least 50MHz. Many of these probes have amplifiers available to provide the scope with as low as 1mA/div current sensitivity or better. Some probes are capable of 1000 amps. All of them were designed to be connected to oscilloscopes for observing the current waveform. But most of them can be used with digital multimeters for accurate measurement also, especially if the DMM uses true-RMS measurement techniques or the waveform is known to be a sine wave.
The passive AC probes were designed to work into a passive termination or into a current probe amplifier such as the model 134. The 7000-series of lab scopes of the 1970s had the 7A14 current probe amplifier plug-in that looked much like the usual vertical preamps but was designed specifically to use passive AC probes.
Dean
Tektronix has provided more methods of DC and AC current measurement that probably any other company. They have passive AC current probes (HF transformers in the heads) that are good from around 500 Hz to over 250MHz, depending upon the model. These probes also have fantastic pulse characteristics. They have DC/AC probes (Hall-effect sensors in the heads) that are good from DC to at least 50MHz. Many of these probes have amplifiers available to provide the scope with as low as 1mA/div current sensitivity or better. Some probes are capable of 1000 amps. All of them were designed to be connected to oscilloscopes for observing the current waveform. But most of them can be used with digital multimeters for accurate measurement also, especially if the DMM uses true-RMS measurement techniques or the waveform is known to be a sine wave.
The passive AC probes were designed to work into a passive termination or into a current probe amplifier such as the model 134. The 7000-series of lab scopes of the 1970s had the 7A14 current probe amplifier plug-in that looked much like the usual vertical preamps but was designed specifically to use passive AC probes.
Dean
