HANDHELD DATA-LOGGER SPECIFICATIONS

Specifications for the Gx Data-Logger

Given the nature of the environments in which site surveys (annual & bi-monthly surveys) are typically conducted and the nature of the actual voltages that are logged by data-loggers on these types of surveys, the voltmeter component of the data-logger has to satisfy a number of important performance criteria.

Voltmeter Specifications

The performance criteria that are particularly significant for a voltmeter employed in site survey work are as follows:

High Voltage Isolation.

Since site surveys are typically conducted in the vicinity of electrical devices and power line systems, and, since transient over-voltages can occur frequently and at high levels in today’s electrical systems, it is imperative that a high degree of voltage isolation be provided to ensure operator safety.

The IEC (International Electrotechnical Commission) has specified that voltmeters employed in Category IV environments, which are environments typically encountered during site survey work (outside areas in the vicinity of electrical devices and power lines), must provide at least 1kV isolation (steady-state voltage) and at least 12kV transient (momentary) overload protection. It is critical that purchasers of data-loggers that are intended for use in such environments be aware of these (minimum) requirements.

The M. C. Miller Co. (MCM) voltmeter, which is used in all MCM data-loggers including the Gx, is designed for 3kV (steady-state) isolation (tested to 1kV) and 50kV transient voltage isolation (tested to 15kV), and thus is designed to exceed the IEC Standard for Category IV environments. On the other hand, the National Instruments voltmeter models (PCMCIA NI4050 and NI4060) provide no high voltage isolation, while model NI4070 only provides up to 300V (steady-state) isolation. [NI voltmeter cards are used, for example, in Allegro data-loggers]. Consequently, it is imperative, from an operator’s safety standpoint, to be aware of the specific voltmeter PCMCIA card that is employed in any data-logger you might be considering for site survey work and to be aware of any associated liability issues.

Voltmeter Response Time and Resolution.

In cases where fast rectifier current interruption cycles are to be in-effect during surveys [on the order of 1Hz, for example (perhaps 0.7 sec. On/0.3 sec. Off cycles)], it is imperative that the voltmeter response time be fast in order that true On/Off voltages can be measured.

It is particularly important that the response time be fast even when the input impedance of the voltmeter is on a high setting.  A high input impedance setting is required for a voltmeter when the source resistance associated with a measurement is high, for example, in a high soil resistivity situation, in order that a voltage measurement is not affected by the source resistance and a true reading is presented.

Consequently, in site survey work where poor contact (of reference electrode data-probe with the soil) can occur and high soil resistances can be encountered (both of which impact the “source resistance”), it is important to employ a voltmeter that has a high input impedance setting option. In addition, it is critical, in the case of fast interruption cycling, that the high input impedance setting also be a fast response setting. Furthermore, the voltmeter setting should also provide a high resolution (high degree of accuracy).

The MCM voltmeter has a setting which satisfies all three of these criteria simultaneously, which is the 5.7Volt, 400MΩ setting. This setting provides a response time of 80ms and a resolution of 0.17mV, while presenting an input impedance of 400MΩ.

Noise and AC Interference Filtering on Fast Cycle Setting.

Since AC interference and noise can be encountered on buried pipelines, it is imperative that the voltmeter does not saturate at the voltage levels that might typically be induced, which would lead to erroneous On/Off pipe-to-soil voltage readings. It is also imperative that the fast cycling On/Off potentials can be “extracted” from the background noise.

The MCM voltmeter will not saturate even with an AC signal as large as 120V appearing at the input and will maintain sufficient speed to process the fast cycle waveform data. The MCM voltmeter accomplishes this feat by using a sophisticated combination of analog pre-processing and digital signal processing (DSP). The sampling rate for the DSP is 3600 times per second.

Other Key Specifications (Hardware & Software):

CATEGORY	Gx  SPECIFICATION
Computer Related Specifications
Rugged Classification	Ultra-Rugged Handheld Computer (Die Cast magnesium alloy and high impact plastic)
Environmental Specifications	Exceeds MIL STD 810F Rating Survives 6 foot drops to concrete IP 67 Rating (dust/water intrusion) Operating Temp. -4°F to 122 °F (-20°C to 50°C) Storage Temp. -4°F to 140°F (-20°C to 60°C)
Processor	Xscale processor (624MHz)
Memory	256MB SDRAM;
Non-Volatile File Storage (including survey files)	2GB SD card
Operating System	Windows CE 5.0
Main Power Supply	Two re-chargeable 2500mAh Li-Ion batteries (5000mAh total capacity)
Battery Life (Main Power Supply)	40+ hours continuous operating
RAM Retention (survey programs are stored on RAM)	If main battery pack is allowed to fully-discharge or is being replaced, a back-up battery provides 40 hours of RAM retention time.
Display Screen	320x240 pixel (3.5 inch) color LCD touch-screen (indoor/outdoor viewing)
Communication Port (for survey data)	Serial (RS232) & USB ports, Bluetooth-enabled
Dimensions	12.5”(L) x 5.31” (D) x 2.31” (W)
System Weight	2.64 lbs
CP Survey Related Specifications
Annual, bi-monthly etc. Site Surveys (both continuous and current-interrupted)	Yes (Gx-SS app)
Trigger-mode CIS	Yes (Gx-PLS app)
Timer-mode CIS	Yes (Gx-PLS app)
DCVG surveys	Yes (Gx-PLS app)
Combined DCVG/CIS surveys	Yes (Gx-PLS app)
Stationary data-logger surveys	Yes (Gx-Time Chart Recorder app)
Internal GPS receiver	Yes
External GPS receiver ready	Yes
Built-in MCM Voltmeter Specifications
Options for DC range and input impedance settings	5.7V, 400MΩ  57V, 75MΩ 57V, 400MΩ    570V, 75MΩ 40V, 75MΩ      40mV, 10MΩ 400V, 75MΩ     400mV, 10MΩ
Options for AC range and input impedance settings	40V, 75MVΩ 400V, 75MΩ
Voltmeter reading style options	Single reading On/Off pairs On/Off pairs (min/max) On/Off pairs (GPS Sync)

Data Management & Route Management on the Data-Logger

Route data (generated on the ProActive side), including sites to be visited, readings to be taken at each site, and reading templates for each reading type, are downloaded to the Gx data-logger via an ActiveSync connection between the logger and a PC (or laptop) running ProActive Client. Each route is downloaded as a separate file and is stored on the logger’s CompactFlash memory card (a non-volatile memory). Previous readings data for each site are downloaded with the route data and are presented on each reading prompt screen for comparison purposes with the current readings. The site survey information screen on the logger indicates the date the survey was started and the date the survey was completed, the total number of sites to be visited, the number of sites completed at any given point and the number of non-compliant sites, based on compliance criteria entered on the ProActive side for each reading type. For example, a reading may be flagged if the current reading differs from the previous reading by a certain percentage value (say, 10%). Such flags are posted back to ProActive and are readily available in a single table (on a line segment basis) from which To-Do List reports can conveniently (and easily) be generated.

Multiple routes (multiple files) can be stored (permanently) on the CompactFlash memory card. Prior to starting a particular site survey on a given route, a technician downloads the route data (from ProActive) to the logger in order to have the (latest) previous readings data on the logger for comparison purposes. When downloading route data, the data-logger updates the route file on the CompactFlash card if the route file is correctly saved on the logger.

When a site survey has been completed on a given route, ProActive acquires the readings data (via an ActiveSync connection) and posts them to the appropriate sites in the database, where they are integrated with historical data. Once stored in the ProActive database, a multitude of graphs can be generated, based on the readings data, including reading type data (for example, rectifier volts and rectifier amps) plotted versus survey date or reading type data plotted versus location, for example, annual pipe-to-soil readings versus site location (station number or milepost). In addition, such data can be graphed on a year-over-year basis.

The integrated relationship between the data-logger, ProActive Client and the database is illustrated in the figure over-leaf.

Data Entry Mechanisms

There are a variety of ways that a technician can enter data into the logger. Data can be entered by tapping the “Read” button on a reading type prompt screen using the stylus or by pressing the “Enter” key on the keypad.

If an MCM reference electrode data probe is being used for pipe-to-soil readings, data can conveniently be entered by pressing the push-button trigger on top of the data-probe handle.

Data can also be entered manually on the prompt screens using the keypad. For example, if a prompt calls for a soil resistivity reading, such data can be obtained using appropriate instrumentation and the reading can be entered manually on the data-logger.

GPS Capabilities

The Gx data-logger comes equipped with an internal WAAS-enabled GPS receiver for convenient logging of site location data. Posted GPS position data can be employed by ProActive Client to generate reports that include topographical, photographical or street maps with the sites suitably arrayed on an overlaid pipeline. Also, external (NMEA-compatible) GPS receivers, such as Trimble Pathfinder receivers, can be integrated with the Gx.

Data-Logger Software Licensing

A software license is required (for each data-logger) to run the MCM survey application programs on the logger. The license can be leased on an annual basis or can be purchased outright (see “System Pricing” Section).

With an annual lease option, the annual license fee includes customer support services and also periodic data-logger software updates, including enhancements and new features (typically offered 2 or 3 times per year).

With an outright license purchase, an annual subscription can also be purchased which would provide for customer support services and the periodic data-logger software updates.

The Gx data-loggers come with a 12 month parts and labor warranty.