The Challenge:

Implementing a large channel remote data logging system that can display real time trending of a number of critical channels on different PC’s on the Network. The distance between the test area and control room is over a kilometer and hence wiring individual thermocouples (about 200) to the control room is to be avoided.

The Solution:

The Remote data logging system was developed on LabVIEW RT 6.1 with PXI-8145 RT Controller and signal conditioning is provided by SCXI-1112 Thermocouple amplifier. This system could thus act as a remote data acquisition and storage unit, which is rugged and reliable. The data from this system is sent out over a Fiber Optic Network to the control room in real time and PC’s on a Local Area Network in the control room can monitor the temperature on-line.

Introduction:

The remote data logging system is a 208 channel data logger configured with 26 numbers of SCXI- 1112 modules. Since the test site is over a kilometer away from a human operator, a rugged and unattended system configuration was required. The logging of temperature data is to be performed in a harsh environment with high level of vibration. Hence a logging system was required which will withstand these conditions without any loss of data or failure. Also on-line monitoring of critical channels of the acquired data is one of the important requirements.

System Configurations:

The system consisted of PXI-8145 RT Controller in a PXI-1011 Chassis with eight SCXI-1112 Modules. The communication to these eight modules is established via SCXI internal back-plane with the help of PXI-6040E Multifunction Data Acquisition Card. The additional modules are place in two SCXI-1001, 12-Slot Chasses. The control room setup consisted of a host PC where the entire channel related configuration is performed, the acquisition and logging program is then downloaded to the PXI-8145 RT controller. An overview of the system is shown in Figure 1.

System Description:

The temperature data logging system consists of Channel Configuration, Thermocouple Continuity Checking, Data Acquisition and logging, Graphical and Digital Displays, Test Number entry, Data logging, Processing of logged data for report generation and Offline printing of logged data in graphical format.

Data acquisition is based on a channel configuration file that the user creates. The created configuration file is stored in a folder created with Test number. User has the option to Create, Open and Save Configuration files. Channel configuration consists of Channel Identifying name, Channel Description, Thermocouple Type, Temperature Unit, Logging precision and Scan Rate.

Along with the temperature channel an additional channel is also logged. This channel is used for identifying the instance from which the data is important. The level of the signal identifies this and assigns zero as the time stamp for the data. Duration of Data Acquisition is also specified in the channel configuration.

Before the acquisition begins thermocouples are checked for continuity and noise level. This is achieved by viewing the acquired Temperature data, Peak-to-Peak voltage, RMS and Average voltage of 8-channels at a time. This is also displayed on the host PC’s so that people in the control room are aware of any defective thermocouples or open circuits before the start of any test.

Data acquisition is performed based on the channel configuration file information. The configuration information is transferred to the PXI-RT through TCP/IP. Graphical displays are provided in each of the host computers with up to 4 charts. Each chart can have a maximum of 4-plots. The plots are user selectable for each chart. Thus the trending of up to 16 channels can be monitored on each PC. Digital displays are provided for each indicator channel, which is also user selectable. A typical screen is shown in Figure 2.

Test Number is entered at the start of the test. Test Number will be used for creating folder in which data files are stored. Actual data logging is carried out in the PXI-RT and once the data acquisition time is over the data file is automatically transferred to the host through File Transfer Protocol (FTP). The data file is transferred to the “Test Number” folder. Data for Monitoring though is sent to the hosts on-line through real time TCPI/P protocol.

For report generation the raw data file is processed to rearrange the time stamp and remove any temperature offset. Based on this logged data processed file sub-files are created with any combination of channels and time range these files later printed in graphical format

Conclusion:

The Embedded controller based PXI-RT Combined with SCXI-1112 provided an extremely reliable, rugged and low cost real-time temperature logging system. The system could handle a large number of channels and provided options for further expansion. Using a Network based remotely power-able UPS and the calibration features of the SCXI allowed the user to power-on, calibrate, check for continuity and acquire data without having to go to the remote sit at all.