Test Products International (TPI)

Frequently Asked Questions

Oscilloscope Probes FAQs

Why is common rejection ratio (CMMR) important for differential probes?

CMMR is a measure of how well a differential probe will reject signals common to both test points, leaving the desired signal to be displayed by the scope.

What is the benefit of a probe with X1 and X10 switchable attenuation?

Passive X10 probes allow you to read a signal 10 times the amplitude of that viewed with a X1 probe. Example: an eight-division graticule on 5V/Div setting would display a 40 volt peak-to-peak signal using the X1 setting. You can view a 400 volt signal using the X10 setting.

Why do TPI oscilloscope probes have a compensation range and compensation adjustment?

Since the input of every oscilloscope is different our probes have a compensation adjustment so the capacitance of the probe can be adjusted to match the capacitance of the scope input. The compensation range is the range of adjustment available. Matching probe and scope capacitance is important to prevent waveform distortion.

Test Leads FAQs

What are important specifications when considering test leads?

Strands of wire

  • The more strands of wire in a test lead, the more flexible it typically is.
  • Higher strand count increases test lead life.
  • TPI silicone insulated test leads offer higher strand counts than PVC insulated leads.

PVC Insulated test leads

  • Durable low cost lead.
  • Useful for general test and measurement applications.

Silicone Insulated test leads

  • Most durable test lead.
  • Double insulated for safety. When half the insulation is worn away or when a lead is nicked or cut, you will see a white strip. This strip indicates half the insulation is gone and the lead should be replaced.
  • Flame retardant. PVC test leads will burn or melt when exposed to heat.
  • More flexible than PVC leads.
  • Typically carry agency approval such as: cULus and IEC category ratings

Tech Tips

Oscilloscope Probes & SMTP Clips TECH Tips:

Several important factors must be taken into account when selecting the proper probe:

  • The probe should have sufficient bandwidth and rise time for the test instrument and application. Choose a probe with at least an equal bandwidth as the scope it will be used with. For best performance a probe with twice the bandwidth as the scope should be selected.
  • For oscilloscope probes, the input capacitance of your oscilloscope should be within the compensation range specification of the probe. In addition, if your oscilloscope has readout function, select a probe with this capability.
  • For differential probes, make sure the maximum differential voltage is adequate for your application and the common mode rejection specification meets the requirements of the tests being performed.


  • Attenuation: Ratio of the output signal to the input signal. Attenuation should remain constant decreasing by 3dB only as the frequency increases to the maximum bandwidth.
  • Bandwidth: The maximum -3dB frequency that can be expected.
  • CMRR (Common Mode Rejection Ratio): A measure of a differential probes ability to reject any signals common to both test points in a differential measurement
  • Compensation Range: The range a probe can be compensated to match the input capacitance of the test equipment it is being used with.
  • IEC 1010: Probes with the IEC 1010 category rating have been designed for safety.
  • Input Impedance: The total resistance and capacitance as measured at the tip of the probe. This specification is used to define the loading effect of a probe. At frequencies under 1MHz the input resistance of the probe will have the most influence. At higher frequencies the input capacitance will have the most influence.
  • Readout: Probes with this capability are compatible with readout function oscilloscopes that automatically detect and display the attenuation factor of the probe.
  • Rise Time: The time required for the leading edge of a pulse to rise from 10% to 90% of its final value.