The Model 197A is a six function, 5-1/2 digit resolution autoranging digital multimeter with a ±220,000 count LCD (Liquid Crystal Display). This A/D range is greater than the normal ±199,999 count A/D used in many 5-1 /2 digit DMMs. The 5-1 /2 digit resolution allows the Model 197A to measure DC voltage for 1µV/count to 1000V. AC voltage and current measurements are standard in the Model 197A. TRMS ACV capability ranges from 1µV/ count to 750V. The Model 197A measures resistance from 1mΩ. to 220MΩ on seven resistance ranges. The Model 197A has six current ranges that measure current from 1nA (10⁻⁹A) to 10A. The dB function makes it possible to compress a large range of readings into a much smaller scope. Model 197A dBm measurements can be referenced to 50, 75,93,135, 300 or 600Ω (default), but can be modified with the use of the relative (REL) feature. The Model 197A has two IEEE-488 interface options: The Model 1972A and the Model 1973A. These optional interfaces enhance the capabilities of the Model 197A by allowing programmed control over the IEEE-488 bus. The Model 1972A also includes an analog output. The bus commands are the same for each interface and respond to IEEE-488 protocol. The Model 197A includes the following features: 1. Six Measurement Functions — DCV, ACV, DC A, ACA, OHMS and dB all built in. 2. (REL) Relative Mode — The relative mode allows offsets to be nulled out (e.g. test lead resistance for low resistance measurements) and selects a variety of reference impedances for dB measurements. 3. Digital Calibration — A non-volatile RAM stores calibration constants and can be performed from the front panel or over the IEEE-488 bus. 4. Data Logger — A data storage buffer is included to allow up to 100 readings and minimum/maximum readings be internally stored at a user selectable rate. The buffer may be read and controlled from the front panel or over the IEEE-488 bus. In the talk-only mode, the output rate can also be programmed. 5. Autoranging — The Model 197A includes a fast autoranging feature for easier measurements. 6. 5-1/2 Digit Resolution — The Model 197A has a ±220,000 count A/D that surpasses the more common ±199,999 count A/D. 7. Four Terminal Ohms — These terminals are used to eliminate the voltage from across the current carrying leads. 8. Sensitivity — The Model 197A has 1µV, lmΩ and 1nA sensitivity. The 1µV of sensitivity allows minute levels of offset, temperature etc. A 1nA sensitivity allows low current measurements without special equipment. Measure leakage, bias and offset current. A 1mΩ sensitivity allows easy low resistance measurements. 9. Electroluminescent Display Backlight — A switch selectable electroluminescent display backlight used to enhance the liquid crystal display under low light or dark conditions. 10. dB Reference Impedances — Selectable dB reference impedances of 50Ω, 75Ω, 93Ω,135Ω, 300Ω and 600Ω (default).