Keithley 2015/J - 6.5 Digit Total Harmonic Distortion Digital Multimeter

• Maximum Resolution: 6.5 digit
• Frequency domain analysis in conventional time domain instruments
• Dual output audio band sine wave source
• Fast frequency sweeps

The 2015/J Total Harmonic Distortion Multimeter combine audio band quality measurements and analysis with a full-function 6½-digit DMM. Test engineers can make a broad range of voltage, resistance, current, frequency, and distortion measurements, all with the same compact, half-rack measurement instrument.

Frequency Domain Distortion Analysis

For applications such as assessing non-linear distortion in components, devices, and systems, DSP-based processing allows the 2015/J to provide frequency domain analysis in conventional time domain instruments. They can measure Total Harmonic Distortion (THD) over the complete 20 Hz to 20 kHz audio band. They also measure over a wide input range (up to 750 Vrms) and have low residual distortion (–87 dB). The THD reading can be expressed either in decibels or as a percentage.

In addition to THD, the 2015/J can compute THD+Noise and Signal-to-Noise plus Distortion (SINAD). For analyses in which the individual harmonics are the criteria of greatest interest, the instruments can report any of the (up to 64) harmonic magnitudes that can be included in the distortion measurements. The user can program the actual number of harmonics to be included in a computation, so accuracy, speed, and complexity can be optimized for a specific application. (See Figure 1.)

Optimized for Production Testing

The 2015/J can perform fast frequency sweeps for characterizing audio-band circuitry in production test systems. For example, the instruments can execute a single sweep of 30 frequencies and transmit both rms voltage readings and THD readings to a computer in only 1.1 seconds. With that data, a complete frequency response analysis and a harmonic distortion vs. frequency analysis can be performed in a very short time. Thus high speed testing of the audio performance of a high volume device such as a cellular telephone can be performed without reducing the number of tests or reducing the measurements in each test. With these instruments, which are optimized for production testing, test engineers can lower test times, in comparison to test speeds achievable with general purpose audio analyzers, without sacrificing production test quality.

Figure 1. Frequency Spectrum of 1kHz Square Wave. Figure 1 shows a plot of a square wave’s harmonics (frequency components) computed and transmitted to a personal computer by the 2015/J. A square wave’s spectral content consists of only odd harmonics whose magnitudes are (1/harmonic number × the magnitude of the fundamental). For example, the magnitude of the third harmonic is 1⁄3 the magnitude of the fundamental.

Figures 2, 3, and 4 demonstrate how the 2015/J can provide both time domain and frequency domain measurements in a single test protocol. Figure 2 shows a sample test system schematic with a telecommunication device in a loop back mode test. The Audio Analyzing DMM’s source provides a stimulus frequency sweep, and the Audio Analyzing DMM measures the response from the microphone circuit. Figure 3 shows the resulting frequency domain analysis of the THD and the first three harmonics as a function of frequency. Figure 4 shows the time domain analysis of microphone circuit output voltage as a function of frequency.

Figure 2. Total Harmonic Distortion Analysis and Frequency Response of a Portable Wireless Telecommunication Device

Figure 3. THD and 2nd, 3rd, and 4th Harmonics as a Function of Frequency

Figure 4. Frequency Response

Dual Output Source

The 2015/J include an internal audio band sine wave source for generating stimulus signals. A second output, the inverse of the first output, is also available, simplifying the testing of differential input circuits for common mode or noise cancellation performance. The 2015/J have a 4 Vrms single-ended output and 8 Vrms differential source output.

Wide Selection of Audio Filters

Five industry-standard bandpass filters are provided for shaping the input signal for audio and telecommunication applications. Available filters include the CCITT weighting filter, CCIR filter, C-message filter, CCIR/ARM filter, and :A" weighting filter (see Figures 5a–5e). The 2015/J provide programmable, high cutoff (low pass) and low cutoff (high pass) filters. Furthermore, the two filters can be implemented together to form a bandpass filter. The programmable filters can be used to filter out noise generated by electromechanical machinery on the production floor or to simulate other types of system transmission characteristics.

Figure 5a.

Figure 5b. 

Figure 5c.

Figure 5d.

Figure 5e.

Broad Measurement Flexibility

In addition to their THD, THD+Noise, SINAD, and individual harmonic measurement capabilities, the instruments provide a comprehensive set of DMM functions, including DCV, ACV, DCI, ACI, 2WΩ, 4WΩ, temperature, frequency, period, dB, dBm, and continuity measurements, as well as diode testing. This multifunctional design minimizes added equipment costs when configuring test setups.

Wide Band or Narrow Band

Noise Measurements The 2015/J are capable of measuring both wide band noise and narrow band noise. Alternatively, these instruments’ DSP (digital signal processing) capabilities allow users to make frequency domain measurements of RMS voltage noise over the 20 Hz–20 kHz frequency audio band or a narrow portion of the band. Furthermore, noise measurements can be extracted in the presence of a stimulus signal for fast signal-to-noise computations.

Keithley 2015/J Rear Panel