Field service engineers require many different load cells spanning the different ranges necessary to calibrate their customers’ systems. They may also need the assortment to conduct a variety of force measurements for the testing application. The challenge begins when the engineer needs to modify the load cell that is connected to his instrument before he can continue. When the multi axis force sensor is linked to the instrument, the correct calibration factors need to be placed in the instrument.
Avoiding user-error is actually 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, or perhaps worse, corrupting the current calibration data, can lead to erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the load cell being connected to it and self-installing the correct calibration data is optimal.
Precisely 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 which include common, network-independent communication interfaces to connect transducers to microprocessors and instrumentation systems.
With TEDS technology, data may be stored on the inside of a memory chip that is certainly installed inside of a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a large number of detailed electronic data templates with many amount of standardization. Even while using the data templates, it is far from guaranteed that different vendors of TEDS-compliant systems will interpret what data is put into the electronic templates in a similar manner. Moreover, it is not apparent that the calibration data that is required in your application is going to be backed up by a certain vendor’s TEDS unit. You have to also be sure that you have a means to write the TEDS data in to the TEDS-compatible load cell, through a TEDS-compatible instrument that has both TEDS-write and TEDS-read capabilities, or with the use of a few other, likely computer based, TEDS data writing system.
For precision applications, such as calibration systems, it also need to be noted that calibration data that is stored in the load cell is identical no matter what instrument is attached to it. Additional compensation for your instrument is not included. Matched systems in which a field service calibration group may be attaching different load cells to several instruments can present a problem.
Electro Standards Laboratories (ESL) has developed the TEDS-Tag auto identification system which retains the attractive feature of self identification based in the TEDS standard but could be implemented simply on any load cell and, when attached to the ESL Model 4215 smart meter or CellMite intelligent digital signal conditioner, becomes transparent towards the user. Multiple load-cell and multiple instrument matched pair calibrations will also be supported. This may be a critical advantage in precision applications such as field calibration services.
Using the TEDS-Tag system, a tiny and inexpensive electronic identification chip is positioned 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 may be read from the ESL Model 4215 or CellMite to distinguish the cell. The cell will be linked to the unit as well as a standard calibration procedure is conducted. The instrument automatically stores the calibration data inside the unit itself together with the load sensor identification number through the microchip. Whenever that cell is reconnected towards the instrument, it automatically recognizes the cell and self-installs the correct calibration data. True plug-and-play operation is achieved. With this particular system the calibration data can automatically include compensation for that particular instrument so that high precision matched systems could be realized. Moreover, when the cell is transferred 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 in to a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is readily provided by distributors or from ESL. The chip is extremely small, which makes it very easy to fit into a cable hood or cell housing.
Both ESL Model 4215 smart strain gauge indicator as well as the CellMite intelligent digital signal conditioner are linked to load cells by way of a DB9 connector with identical pin outs. The electronic identification chip will not affect the cell’s signals. Pin 3 from the DS2401 will not be used and will be shut down if desired. Simply connecting pins 1 and two from your DS2401 to pins 8 and 7, respectively, from the ESL DB9 connector will enable plug-and-play operation.
When you use off-the-shelf load cells, it is often convenient to locate the DS2401 in the hood of the cable. The cell features a permanently mounted cable that protrudes through the cell housing. At the end of the cable, strip back the insulation from the individual wires and solder the wires in to the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits inside the connector’s hood. For a couple dollars in parts as well as a simple cable termination procedure, you might have taken a typical load cell and transformed it right into a TEDS-Tag plug-and-play unit.
For applications in which access to the 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 in fact put into series with the load cell cable before it is connected to the ESL instrument. It is additionally possible to make use of this technique in applications where different calibrations may be required on the same load cell. The ifegti could have a single load cell and instrument, but could change which calibration is auto-selected by just changing the in-line cable adapter. Since each cable adapter includes a different tag identification chip, the ESL instrument will associate another calibration data set with every in-line adapter. This can be useful, for instance, if a precision 6-point linearization in the load cell is needed by two different operating ranges the exact same load cell.
Given that the burden cell has been converted to a TEDS-Tag unit, it could be attached to the ESL Model 4215 smart strain gauge indicator or a CellMite intelligent digital signal conditioner. The first time that it is connected, a regular calibration procedure is performed to initialize the cell’s calibration data inside the instrument. The ESL instruments support a variety of industry standard calibrations including mV/V, shunt, 2-point, or multiple-point calibration. The instrument then automatically detects the actual existence of the force transducer and matches it featuring its calibration data. From this point forward, the device is completely plug-and-play.