Load Cell – You’Ll Want To See This..

Field service engineers require a variety of load cells spanning the numerous ranges necessary to calibrate their customers’ systems. They may also require the assortment to conduct an array of force measurements for a particular testing application. The process begins when the engineer needs to modify the load cell that is attached to his instrument before he is able to continue. If the new cell is connected to the instrument, the appropriate calibration factors have to be installed in the Force Transducer.

Avoiding user-error is a major challenge with manual data entry or with requiring the engineer to pick from a database of stored calibration parameters. Loading a bad parameters, as well as worse, corrupting the current calibration data, can result in erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the burden cell being connected to it and self-installing the appropriate calibration information is optimal.

What is Transducer Electronic Datasheet? A Transducer Electronic Data Sheet (TEDS) stores transducer identification, calibration and correction data, and manufacturer-related information in a uniform manner. The IEEE Instrumentation and Measurement Society’s Sensor Technology Technical Committee developed the formats including common, network-independent communication interfaces for connecting transducers to microprocessors and instrumentation systems.

With TEDS technology, data could be stored on the inside of a memory chip which is installed on the inside of a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a huge number of detailed electronic data templates with a few level of standardization. Even while using the data templates, it is really not guaranteed that different vendors of TEDS-compliant systems will interpret what data enters into the electronic templates in a similar manner. More importantly, it is far from apparent that this calibration data that is needed in your application will be supported by a particular vendor’s TEDS unit. You need to also be sure that you have a means to write the TEDS data into the TEDS-compatible load cell, through a TEDS-compatible instrument that has both TEDS-write and TEDS-read capabilities, or by using some other, likely computer based, TEDS data writing system.

For precision applications, including calibration systems, it ought to be noted that calibration data that is stored in the load cell is identical regardless of what instrument is linked to it. Additional compensation for the Torque Transducer itself is not included. Matched systems in which a field service calibration group could be attaching different load cells to various instruments can present a difficulty.

Electro Standards Laboratories (ESL) has evolved the TEDS-Tag auto identification system which retains the attractive feature of self identification based in the TEDS standard but may be implemented simply on any load cell and, when connected to the ESL Model 4215 smart meter or CellMite intelligent digital signal conditioner, becomes transparent for the user. Multiple load-cell and multiple instrument matched pair calibrations are also supported. This is often a critical advantage in precision applications such as field calibration services.

With the TEDS-Tag system, a small and inexpensive electronic identification chip is placed in the cable that extends through the load cell or it may be mounted in the cell housing. This chip has a unique electronic serial number that can be read through the ESL Model 4215 or CellMite to identify the cell. The cell is then connected to the unit and a standard calibration procedure is conducted. The instrument automatically stores the calibration data inside the unit itself together with the unique load cell identification number through the microchip. Whenever that cell is reconnected towards the instrument, it automatically recognizes the cell and self-installs the appropriate calibration data. True plug-and-play operation is achieved. Using this system the calibration data can automatically include compensation for your particular instrument in order that high precision matched systems can be realized. Moreover, if the cell is moved to another instrument, that instrument will recall the calibration data that it has stored internally for that load cell. The ESL instruments can store multiple load cell calibration entries. This way, multiple load cells can form a matched calibration set with multiple instruments.

Any load cell can easily be made right into a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is readily offered by distributors or from ESL. The chip is quite small, which makes it easy to fit into a cable hood or cell housing.

Both the ESL Model 4215 smart strain gauge indicator and the CellMite intelligent digital signal conditioner are connected to load cells via a DB9 connector with identical pin outs. The electronic identification chip does not hinder the cell’s signals. Pin 3 of the DS2401 will not be used and may be cut off if desired. Simply connecting pins 1 and two from the DS2401 to pins 8 and 7, respectively, in the ESL DB9 connector will enable plug-and-play operation.

When using off-the-shelf load cells, it is usually convenient to locate the DS2401 inside the hood in the cable. The cell comes with a permanently mounted cable that protrudes from the cell housing. At the end of the cable, strip back the insulation from your individual wires and solder the wires to the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits inside the connector’s hood. For a few dollars in parts and a simple cable termination procedure, you have taken a regular load cell and transformed it right into a TEDS-Tag plug-and-play unit.

For applications where accessibility load cell and cable is fixed, an in-line tag identification module may be simply constructed. A straight through in-line cable adapter can incorporate the DS2401 electronic tag chip. In this application, the cable adapter is really positioned in series with all the load cell cable before it is actually plugged into the Load Cell. It is also possible to use this technique in applications where different calibrations might be required on the same load cell. The consumer may mbssap a single load cell and instrument, but can change which calibration is auto-selected by simply changing the in-line cable adapter. Since each cable adapter has a different tag identification chip, the ESL instrument will associate an alternative calibration data set with each in-line adapter. This might be useful, for example, when a precision 6-point linearization of the load cell is necessary in two different operating ranges of the same load cell.