2640A/2645A NetDAQ

Users Manual

reading rate and scan interval that is an exact multiple of the power line period and cause line frequency noise to be aliased to a very low frequency, where it appears as drift, or instability, in the readings. For example, if the instrument is set to Reading Rate = Fast and a scan interval of 100 ms, line frequency noise is aliased because the scan interval is an exact multiple of the period of the power line.

One way to see whether your measurement setup has a potential problem like this is to pick a scan interval like 98 ms or 102 ms, that is not an exact multiple of the power line period. If the readings appear noisier with this scan interval than with an interval of 100 ms, there is a problem with the measurement setup. Possible solutions to this problem are:

1.Use shielded wiring to prevent power line noise pickup from mixing with the signal. Be sure the shield is connected to an earth ground.

2.Route signal wiring away from power mains wiring.

3.Remove noise from the signal using filters before the signal is applied to the instrument.

4.Select Reading Rate = Slow, which allows the instrument to filter out the noise.

5.Ensure that the chassis of the instrument is connected to earth ground. This is desirable for reasons of safety as well as noise.

Crosstalk Considerations

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The accuracy of low voltage measurements (e.g., thermocouples), low voltage ac measurements and resistance measurements above 3 kΩ can be greatly affected by undesired pickup from ac voltage sources (crosstalk). To reduce the effects of crosstalk, consider each of the following:

1.Reading Rate Do not use Reading Rate = Fast when mixing vac or frequency inputs with low level vdc, thermocouple, and/or resistance inputs. If you must use Reading Rate = Fast, compare a set of readings taken with Reading Rate = Slow against a set of readings taken on the Fast rate to determine the effects of crosstalk on your setup. Measurements made at the Fast reading rate are more susceptible to crosstalk than readings taken at the Slow reading rate.

Note

When you use the Fast rate, it is very easy to get noise into your readings. The Fast rate makes it possible to look at rapidly changing events, but it requires extreme care to keep the readings clean.

2.Shielded Wiring Crosstalk can occur outside the instrument as well as inside the instrument. Use shielded wiring and tie the shields to an earth ground to prevent noise from being coupled into your measurements. Be careful about

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Fluke 2645A, 2640A user manual Crosstalk Considerations
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2645A, 2640A specifications

The Fluke 2640A and 2645A are advanced bench multimeters that represent a significant leap in measurement technology, designed primarily for electrical engineers and technicians who require precision and reliability in their readings. These multimeters are built to cater to complex applications in manufacturing, research, and development.

One of the standout features of the Fluke 2640A and 2645A is their high accuracy. With specifications that can reach up to 0.0035% DC Voltage accuracy, users can trust that their measurements will be consistent and precise. This is especially critical in fields like automated test equipment (ATE) where exact measurements can be crucial for product quality and safety.

Both models incorporate a large, easy-to-read display, making it convenient for users to view measurement results clearly from a distance. They also feature a wide measurement range, capable of handling a variety of tasks, from basic voltage and current measurements to more complex tasks such as resistance and temperature measurements with appropriate sensors.

The multimeters also stand out with their advanced data logging capabilities. The Fluke 2645A, for instance, can store up to 10,000 readings, allowing for extensive data collection and analysis without the need for constant monitoring. This is beneficial for long-term studies or processes that require continual oversight.

Connectivity is another key characteristic. Both the 2640A and 2645A support USB and RS-232 interfaces, which enable easy integration with computers and other devices for seamless data transfer. This feature is important for engineers who rely on software for data analysis and visualization.

Another notable technology included in these models is the Fluke Connect app compatibility, which allows users to remotely monitor measurements from their smartphones or tablets. This capability provides added flexibility, enabling technicians to work hands-free while still keeping an eye on process measurements.

Additionally, the Fluke 2645A comes with a graphical display option, allowing users to visualize measurement trends over time. This graphical representation can be invaluable for diagnosing issues or observing patterns in data.

In conclusion, the Fluke 2640A and 2645A multimeters offer exceptional performance with their high accuracy, extensive data logging, connectivity options, and advanced visualization capabilities. These features make them indispensable tools for professionals in a variety of fields, ensuring that they can achieve reliable results in their measurement endeavors.
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