Additional Considerations 5

Making Mixed Measurements

average-responding measurement devices display the correct rms reading of 1.0000V (the dc component equals 0). However, consider the 2V (peak-to-peak) square wave.

Both types of measurement correctly display the dc component (0V), but the instrument also correctly measures the ac component (1.0000V). The average-responding device measures 1.111V, which amounts to an 11% error.

Average-responding measurement devices have been in use for a long time; you may have accumulated test or reference data based on such instruments. The conversion factors in Figure 5-3 can aid in converting between the two measurement methods.

Making Mixed Measurements

With multiple channels, Hydra Series II allows mixing of measurement types. But the possibility of the ac signal on one channel affecting measurements on other channels must be considered. This effect is known as cross talk.

The ac volts signal could be either a voltage that is to be measured on another channel (which is known as a normal mode signal) or an ac voltage signal on another channel that is present between the channel inputs and earth ground (which is known as a common mode signal). A common mode signal could occur, for example, if an unshielded thermocouple were to be used to measure the metal case temperature of an ac power line diode.

AC voltage cross talk can affect the various measurement types differently. It can cause other ac voltage measurements to read too high. DC and resistance (OHMS) measurements could either shift or read noisy. Frequency measurements could be noisy, or, in the extreme case, the cross talk frequency could actually become the measured signal.

Cross talk can occur at numerous places: in the device or process being monitored, in the wiring to the Hydra Series II instrument, or within the Hydra Series II instrument itself.

Fortunately, precautions can be taken to provide error-free measurements by minimizing the effects of cross talk. Use the following guidelines to minimize cross talk between ac volts signal inputs and other sensitive channels:

∙Keep any input wiring carrying ac volts signals physically separate from other sensitive channel’s input wiring.

∙Avoid connecting inputs with ac volts signals adjacent to sensitive channel inputs. (Leave unconnected channels between the inputs, if possible).

5-9

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Fluke 2620A, 2625A user manual Making Mixed Measurements
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2625A, 2620A specifications

The Fluke 2625A is a sophisticated data logger designed for a wide range of industrial and laboratory applications. This versatile instrument excels in capturing and monitoring temperature and voltage measurements with precision and reliability. One of its standout features is its ability to record data from various sensors, making it ideal for environments where comprehensive data acquisition is critical.

Equipped with a large LCD display, the Fluke 2625A provides clear and user-friendly access to real-time measurement data. Its graphical interface allows users to visualize trends and monitor readings easily, which significantly enhances usability. The device supports a variety of input types and can connect to thermocouples, RTDs, and other sensors, offering great flexibility for various measurement tasks.

The Fluke 2625A employs advanced measurement technologies that ensure accuracy in data logging. With a high sampling rate, it captures fast-changing signals while maintaining data integrity. The device features a built-in memory that allows for extensive logging, accommodating long-term monitoring tasks without requiring constant oversight. Users can set it to log data at specified intervals, offering customizable solutions for different monitoring needs.

Another significant characteristic of the Fluke 2625A is its robust communication capabilities. The device supports USB and RS-232 interfaces for easy connectivity with computers and other devices, making data transfer and analysis seamless. This feature is especially beneficial for users who need to compile or analyze large sets of data quickly.

Furthermore, the Fluke 2625A is designed with durability in mind. Its rugged construction makes it suitable for challenging environments, including those with high levels of vibration, dust, or moisture. This reliability ensures that the device can withstand the rigors of fieldwork while still delivering accurate measurements.

In summary, the Fluke 2625A is a powerful data logger that combines versatility, accuracy, and reliability. Its user-friendly interface, advanced measurement technologies, and robust design make it an essential tool for professionals in various industries, from manufacturing and HVAC to research and development. Whether monitoring temperature changes in a laboratory or assessing voltage levels in an industrial setting, the Fluke 2625A stands out as a trusted solution for effective data logging and analysis.
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