Floating Oscilloscope Measurements ... And Operator Protection

Monolithic Isolation Amplifiers

Figure 3. - A6905 two-channel isolation amplifier (right); A6907 four-channel isolation amplifier (left). Shown with probes.

The Tektronix A6900 Series monolithic isolation amplifiers (see Figure 3) connect between the oscilloscope and the circuit-under-test. The signal is coupled across an electro-optical isolation barrier, providing the necessary isolation. Monolithic voltage isolators provide multiple channels with different "common" potentials in a convenient portable package. These units are designed to be used next to the measurement instrument where physical separation is not a requirement.

Because multiple channels are contained within a single unit, the cost per channel is lower and the actual circuit-to-instrument connections are simplified.

The A6900 Series monolithic voltage isolators are essential tools for power conversion design. The A6907 and A6909 offer safety, performance, multiple isolated channels (A6907 - four channels, A6909 - two channels), direct connection to the measurement instrument, and simplified controls in a single instrument package.

Total Galvanic isolation is accomplished through the use of electro-optical and optical-electro converters. The isolator chassis is referenced to ground to ensure safety while making floating measurements.

The A6900 Series isolators feature a bandwidth of 60 MHz and GPIB control (standard on the A6907; available as Option 10 for the A6909), in a compact package. The CMRR is 105 dB (178,000:1) at 60 Hz, 60 dB (1,000:1) at 1 MHz and 50 dB (316:1) at 10 MHz. The 850 V probes plug directly into the isolators and are specifically designed for safe connection to floating circuits and enhanced CMRR.

These microprocessor controlled instruments feature push-button self-calibration of offset and gain for increased accuracy. Coupling and attenuation for each channel can be individually set.

The A6907 and A6909 satisfy third party safety standards.