Ohio Pen - Reading Pulse Output with dataTaker DT8x Data Loggers

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CLEVELAND - OhioPen -- This technical article provides a comprehensive guide to measuring pulse outputs from various sensors using dataTaker DT8x data loggers. Pulse output sensors, commonly found in applications like flow measurement, speed sensing, and power monitoring, generate discrete electrical pulses that represent a specific quantity. Understanding the characteristics of these pulses and the capabilities of the DT8x data logger is crucial for accurate data acquisition.

Here are four common sensor signal output types:

AC Voltage Output: Often found in anemometers and magnetic pickup sensors, these outputs are AC sine waves with varying frequency and amplitude. They require special consideration due to potentially high voltage levels.

Dry Contact Output: Simple switches (mechanical or reed) that require an external voltage source (typically a pull-up resistor) to create a measurable signal. They are commonly used in basic on/off sensing.

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Open Collector Output: Prevalent in industrial automation, these outputs (NPN and PNP) use a transistor to switch between open and ground (NPN) or open and supply voltage (PNP). They also require an external voltage source. Proximity sensors are a typical example.

Voltage Output: These sensors provide a true voltage pulse, often using TTL logic levels (0-0.8V low, 2-5V high) or industrial 24VDC signaling. They can often be directly connected to the data logger.

Flow Meter Example

A turbine flow meter with a dry contact output triggers a reed switch when a magnet in the turbine blade passes by. At a flow rate of 200 GPM, it generates 10,000 pulses per minute, or 167 pulses per second. To record flow every 10 seconds, 1,670 pulses are counted. Due to the simple switch output and pulse frequency (100-200Hz), it's easiest to wire the sensor to a high-speed counter input, such as counter 1.

In deTransfer the program would be:

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BEGIN"JOB1"

CATTN

'Spans and polynomial declarations

S1=0,200,0,1670"GPM"

'Global declarations

RS1S

'schedule definition

RA("B:",ALARMS:OV:100KB,DATA:OV:1MB)10S LOGONA GA

1HSC(R,S1,"Flow")

END

Conclusion

In conclusion, this article provides a valuable resource for selecting the appropriate measurement method for pulse output sensors using dataTaker DT8x data loggers. By considering the sensor output type, signal frequency, and the specific capabilities and limitations of each measurement technique, users can ensure accurate and reliable data acquisition for their applications.

For more information on the dataTaker DT8x family, or to find the ideal solution for your application-specific needs, contact a CAS DataLogger Application Specialist at (800) 956-4437 or visit us at https://www.dataloggerinc.com.