Oscilloscope fundamental
Oscilloscopes translate an electronic signal into a pattern or waveform on a screen. As it is traced across the screen, the waveform creates a signature of the signal’s characteristics. Specifications for oscilloscopes include bandwidth, number of input channels, number of trigger inputs, and resolution. Bandwidth is the frequency range over which oscilloscopes meet their accuracy specifications. Accuracy degrades at lower and lower frequencies unless the oscilloscope is capable of direct current (DC) response. Accuracy also degrades at higher frequencies near resonance and beyond, causing the output response to roll off. The number of input channels is the number of possible, simultaneous signal measurements. Channels can be differential or single-ended. The number of trigger inputs is the number of digital or discrete channels that oscilloscopes use for low-level on-off signals. Resolution refers to the degree of fineness of the digital word representing the analog value. A ten-bit number contains 210 (1024) increments and allows a 0 – 10 V signal to be resolved into approximately 0.01 V increments. A 12-bit representation provides 212 (4096) increments of 0.0024 V for the same signal.
Oscilloscopes use a host interface to communicate with a host computer or other electronic device. Oscilloscopes can use a serial port, parallel port, modem or telephone line, universal serial bus (USB), general-purpose interface bus (GPIB), small computer systems interface (SCSI), or Ethernet connection. Serial ports transfer data one bit a time. RS232, RS422, and RS485 are common serial interfaces. Parallel ports transfer more than one bit at time. Personal computer (PC) printer ports and Centronics ports use parallel communications. Modems (modulators/demodulators) are devices or programs that enable a computer to transmit data over telephone lines. Universal serial bus (USB) is a 4-wire, 12-Mbps serial bus for low-to-medium speed peripheral device connections to personal computers (PC). The general-purpose interface bus (GPIB) is designed to connect computers, peripherals and laboratory instruments so that data and control information can pass between them. Small computer systems interface (SCSI) is an intelligent I/O parallel peripheral bus with a standard, device-independent protocol that allows many peripheral devices to be connected to the SCSI port. Other specialized and proprietary host interfaces for oscilloscopes are also available.
Oscilloscopes provide many different features. Some devices have a relay or switch output for limit detection or other state signalling. Others are powered by a replaceable or rechargeable battery, or are designed to be used while held in one hand. Oscilloscopes that are rated for high-power applications can monitor and/or display currents and voltages associated with electrical power or high-power switching. Typically, these currents and voltages are much higher that standard sensor signal levels. In terms of storage capacity, oscilloscopes can include a hard drive, nonvolatile memory, or on-board random access memory (RAM). Removable storage media devices such as tapes, diskettes, and PCMCIA cards are also available.