Data Logger

Types of Electric Signal available for logging

1. AC Voltage/Current
2. DC Voltage/Current
3. Light On/Off
4. Shock/Acceleration
5. Bridge/Strain/Load/Pressure
6. Motor On/Off
7. Sound
8. Dew point
9. PH
10. Pressure
11. Temperature
12. Event or State
13. Process Voltage/Current
14. Thermistor
15. Frequency
16. Relative Humidity
17. Thermocouple
18. Level
19. RTD

Data loggers benefit users in two ways. They avoid the time and expense of sending someone to take measurements in a remote location, and they enable much higher data density than is achievable through manual recording, providing higher quality data.

Many different types of data loggers are available. They range from single channel devices with the sensor incorporated, to multi-channel loggers capable of acquiring from diverse sensors for extended periods. Data logging software provides the ability to configure acquisition parameters and format data outputs.

How to choose a Data Logger?

Most data loggers are general purpose devices although some are optimized for a specific type of sensor connection and reading (temperature being the most common). A data logging equipment may be selected for one particular task or as an addition to an inventory of data acquisition hardware. In either case, the needs of the intended or likely application(s) should be considered with regard to the following capabilities.

How do data loggers work?

A general purpose multi-channel data logger will usually accept both analog and digital inputs. Examples of analog inputs include temperature, pH and humidity. Note that analog inputs may be either single or double-ended (differential). Using differential sensors halves the number of analog inputs available. An example of this would be a multi channel temperature logger for thermocouples.

Two examples of digital inputs are those from a wind speed sensor or a paddlewheel-style flow sensor. Some types of data logger are designed for specific types of sensor input such as thermocouples or atmospheric sensors (such as barometric pressure and humidity).

Number of Inputs

Data loggers divide into two types: those that accept only a single sensor input (and that sensor may or may not be integrated into the unit), and those that can be connected to a number of sensors simultaneously. While a single channel data logger may be sufficient for some applications the multi-channel data logger is a more versatile device. Multichannel loggers are available with as many as 32 inputs (depending on how the device and sensors are configured). However, the most commonly used type is the 4-channel data logger as this provides a good combination of storage capacity, battery life (where used) and compact size.

Size

In many applications space is a limitation. In those cases the size of the portable data logger may be a critical selection parameter. OMEGA's OM-CP family of data loggers are extremely compact and include models for most input types. Submersible devices are also available for marine and aquatic applications.

Speed/Memory

Data logging systems are available with sampling rates as high as 200 kHz while at the other end of the spectrum some can set to sample once in 24 hours. When evaluating sampling rate requirements note that memory capacity is a fixed number of data points. Thus sampling at a higher frequency fills available memory quicker. Some logger devices handle memory overload by wrapping around and overwriting, which means older data is lost.

Real Time Operation

In general a data logger writes each measurement point to memory for retrieval later. However, some have the ability to output measurement results as they are taken. Look for this feature when it is important to see “live” measurement data.

Data Download

There are several ways of retrieving measurement results from a data logging system. For a simple USB data logger all that’s required is to collect it from the field and plug it into a PC. Data logging software is available to streamline the download process and assist with formatting for Excel® or other packages. If physically visiting the data logger is undesirable but a wired connection is feasible, alternatives are the serial data logger and the RS232 data logger. When running wires out to a remote data logger is infeasible the solution is to use a wireless data logger that transmits data to a receiver connected to a PC.

Key Aspects to Consider When choosing a logging system

1. Input Signal
2. Number of Inputs
3. Size
4. Speed/Memory
5. Real Time Operation

Why Choose a Data Logger Over Other Types of Data Collection Instruments?

Three types of instruments are commonly used for collecting and storing data:

1. Real-Time Data Acquisition Systems
2. Chart Recorders
3. Data Loggers

Other ways of logging measurement data are the chart recorder and the real-time data acquisition system. Until the development of the data logger the chart recorder was the predominant instrument. These typically require pens and specialized paper. Moreover, the data cannot readily be moved into a PC for mathematical or statistical analysis.

Real-time data acquisition systems offer flexibility but also require a direct computer connection. This limits their use in situations where data is to be acquired in a remote location or where portability is a consideration. For example, a realtime data acquisition system would not be feasible in logging temperatures inside refrigerated shipping containers.

Miniature Single Input Data Loggers
Miniature single input data loggers are generally low cost devices dedicated to a specific input type. These types of data loggers are often used in the transportation industry. A typical application would be to include a temperature data logger in a shipment of food products to insure that the food temperature does not exceed acceptable limits. In addition to temperature miniature data loggers are available for a large variety of input types. most input types.

Fixed Mount Multi-Channel Data Loggers
Fixed input loggers have a fixed number of input channels which are generally dedicated for a specific type of input. OMEGA offers fixed input data loggers ranging from one to 8 channels.

Handheld Multi-Channel Data Loggers
Handheld multi-channel loggers are commonly used in applications where the data logger is to be carried from one location to another. They are also commonly used in benchtop or laboratory environments. In addition to storing data internally some models even contain on board printers which can produce an immediate hardcopy of the data.

Modular Data Loggers
A modular data logger is configurable and expandable through the use of plug-in modules. The modules are normally field configurable and the user has the option of adding as many channels to satisfy the application requirement.

What are the Main Advantages of Data Logging?

A data logger provides the ability to take measurements in any location, even during transit, without human intervention. Furthermore, measurements can be closely spaced to capture transient events or far apart to maximize recording duration. Another advantage of data loggers is that the data can then be easily transferred to a PC for analysis and formatting. This significantly reduces the work required to make measurements while allowing for increased data density when needed.

Do Data Loggers Need to be Connected to a Computer?

No, some data loggers provide an option for real-time display but all OMEGA data loggers collect data independently of the computer.

What is the Maximum Sample Rate for a Logger?

The sample rate depends on the specific model. Although most data loggers have a maximum data rate of 1 or 2 samples per second, OMEGA offers a number of data loggers that can sample in excess of 100 samples per second.

How are the logging equipment Powered?

Most data loggers are battery powered some also offer an option for external power.

How Long Does the Battery Powered Logger Last?

The battery life depends on a number of parameters including the specific model and sample rate. In general the faster the sample rate the shorter the battery life. Many OMEGA data loggers feature a battery life as long as ten years.

Will the Data Logger lose its Data if the Power or Battery Fails?

Most OMEGA data loggers use non-volatile memory for data storage. This means that the data will not be lost if the power fails.

How Long Can the devices Record Data?

The recording duration is dependent on the memory capacity of the data logger and the desired sample rate. To determine the duration divide the memory capacity(number of samples the device can record) by the sample rate. As an example assume that a given data logger can store 10,000 samples. If it is desired to record 2 samples every minute, the system can run for 10,000/2 or 5,000 minutes(about 3.5 days). If the sample rate was cut in half(1 sample per minute), the recording period would double to 7 days.