2.1 INTRODUCTION 2.1.1 The Racal-Dana Wideband Level Meter Model 5002 is a light, portable, but extremely versatile, microprocessor controlled instrument. It permits measurements to be made with exceptional accuracy on waveforms having high crest factors. Special automatic zeroing and noise cancelling circuits permit measurements to be made over a range of signal amplitudes extending from 316 V r.m.s. down to 30 uV r.m.s. The instrument has an auto ranging facility, but provision is made for manual range selection. 2.1.2 Measurements may be made on DC signals, on AC signals in the frequency range from 5 Hz to 20 MHz and on signals having both DC and AC components. A low pass filter can be switched in to restrict the operating bandwidth to 200 kHz (~3dB). 2.1.3 The instrument measures true r.m.s., mean, positive peak or negative peak voltages of the applied signal. Operator set values of resistance, voltage and power may be stored in the instrument, and, in addition to display of the measured value in voltage units, displays of the following computed values can be obtained: (a) Average or peak power, computed from V^/R. (b) The ratio of the computed power to the stored power level. (c) The ratio of the measured voltage to the stored voltage level. (d) The difference between the measured and stored voltage levels. (e) The difference between the computed and stored power levels. (f) The difference as in (d) expressed as a percentage of the stored voltage level. (g) The difference as in (e) expressed as a percentage of the stored power level. The instrument will also compute, and display, mean value scaled to r.m.s., peak·-to-peak value, form factor and crest factor. 2.1.4 The input common line is isolated from chassis earth by back-to-back diodes, which permit a voltage difference of ±0.5 V. The common line can be connected to chassis earth, if required, by means of an isolation override switch. 2.1.5 The instrument features a large, four digit, liquid crystal display (LCD). Coarse and fine LCD bar and dot displays form part of the display, and provide a pseudo-analogue form of indication. Units annunciators, GPIB status indicators and instrument status indicators are also incorporated. 2.2 CREST FACTOR 2.2.1 The maximum permitted crest factor on any range increases in inverse proportion to the displayed measurement. Errors will arise if the measured waveform has a significant proportion of its energy in harmonics which lie outside the instrument's measurement bandwidth. 2.3 OPERATING PRINCIPLES 2.3.1 Following a common input attenuator the instrument has separate AC and DC measurement channels. The AC channel features separate detectors for r.m.s., mean, positive peak and negative peak measurements, so that these waveform parameters are all measured simultaneously. 2.3.2 The detector outputs are connected in turn to an analogue to digital converter. The microprocessor scans the converter output every 0.1 second, reading each detector output in turn, One detector output, determined by the measurement function selected, is either converted directly to a display drive signal or processed, together with the contents of various internal stores, to provide power, difference or percentage difference display signals. 2.4 REDUCTION OF DISPLAY JITTER 2.4.1 The instrument has a variable averaging time, which may be set by the operator to ensure minimum jitter of the measurement indication when measurements are made on waveforms of high crest factor. The period over which measurements are averaged may be varied in steps of 0.1 second between 0.1 second and 99.9 seconds (nominal). 2.4.2 The display updating rate is set by the averaging time in use. To avoid the necessity for unacceptably low updating rates, continuous averaging of the measurements can be introduced by means of a special function. In this mode the display is updated every 0.1 second, the new displayed value being formed by adding Ν3ί of the current displayed value to (100-N%) of the new measurement. The effect of this is similar to filtering successive measurements in a single pole RC filter. The value of N is related to the time constant of the effective filter, which can be set by the operator, 2.5 STORAGE OF FRONT PANEL SETTINGS 2.5.1 Provision is made for the storage of up to twelve complete sets of front panel control settings, including the values set in the computed function stores, in a non-volatile memory. Each setting is allocated a number, and is retrieved and set by recalling that number. The front panel control settings in use when the instrument is switched off are automatically stored, and may be recalled when the instrument is switched on again. 2.6 CALIBRATION TO AN EXTERNAL SOURCE 2.6.1 The instrument display may be set to a reference value, when measurements are made on a reference signal source, by means of an operator selected calibration factor. The calibration factor, which is a divisor, is stored in the instrument, and may be enabled and disabled as required when making measurements on other signal sources. 2.7 GPIB INTERFACE 2.7.1 An internally mounted interface board permits the instrument to be controlled from, and communicate with, the IEEE 488 GPIB. The instrument may be used in the addressed mode or in the talk only mode. An adaptor to permit use with the I EC 625-1 GPIB is also available. 2.8 MAINTENANCE 2.8.1 It is recommended that customers should take advantage of the servicing and calibration service offered by Racal-Dana Instruments Ltd., and their agents. For customers wishing to carry out their own servicing, a comprehensive Maintenance Manual is available from Racal-Dana Instruments Ltd. When ordering a manual, the serial number of the instrument for which the manual is required should be quoted.