Field service engineers require a variety of load cells spanning the different ranges required to calibrate their customers’ systems. They may also require the assortment to conduct a wide range of force measurements for the testing application. The challenge begins when the engineer must modify the load cell which is linked to his instrument before he can continue. When the multi axis force sensor is attached to the instrument, the appropriate calibration factors need to be installed in the instrument.
Avoiding user-error is a major challenge with manual data entry or with requiring the engineer from which to choose a database of stored calibration parameters. Loading a bad parameters, as well as worse, corrupting the present calibration data, can result in erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the load cell being mounted on 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 that is installed within a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a huge number of detailed electronic data templates with some degree 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 the same way. More importantly, it is really not apparent that this calibration data that is required within your application will be maintained by a certain vendor’s TEDS unit. You have to also make certain you have a way to write the TEDS data in to the TEDS-compatible load cell, either 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, like calibration systems, it ought to be noted that calibration data that is saved in the load cell is identical no matter what instrument is attached to it. Additional compensation for the instrument is not included. Matched systems when a field service calibration group could be attaching different load cells to different instruments can present a problem.
Electro Standards Laboratories (ESL) has created the TEDS-Tag auto identification system which retains the attractive feature of self identification located in the TEDS standard but may be implemented simply on any load cell and, when linked to the ESL Model 4215 smart meter or CellMite intelligent digital signal conditioner, becomes transparent to the user. Multiple load-cell and multiple instrument matched pair calibrations can also be supported. This may be a critical advantage in precision applications including field calibration services.
With the TEDS-Tag system, a little and inexpensive electronic identification chip is placed in the cable that extends from your load cell or it may be mounted in the cell housing. This chip includes a unique electronic serial number that may be read from the ESL Model 4215 or CellMite to recognize the cell. The cell will be attached to the unit along with a standard calibration procedure is performed. 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 for the instrument, it automatically recognizes the cell and self-installs the proper calibration data. True plug-and-play operation is achieved. With this particular system the calibration data can automatically include compensation for the particular instrument to ensure that high precision matched systems can be realized. Moreover, in the event the cell is relocated 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. In this way, multiple load cells can form a matched calibration set with multiple instruments.
Any load cell can be simply made right into a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is easily available from distributors or from ESL. The chip is extremely small, making it simple to match a cable hood or cell housing.
Both the ESL Model 4215 smart strain gauge indicator and also the CellMite intelligent digital signal conditioner are linked to load cells using a DB9 connector with identical pin outs. The electronic identification chip does not affect the cell’s signals. Pin 3 of the DS2401 will not be used and will be cut off if desired. Simply connecting pins 1 and 2 from your DS2401 to pins 8 and 7, respectively, of the ESL DB9 connector will enable plug-and-play operation.
When utilizing off-the-shelf load cells, it is often easy to locate the DS2401 in the hood from the cable. The cell includes a permanently mounted cable that protrudes from your cell housing. At the conclusion 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 within 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 in to a TEDS-Tag plug-and-play unit.
For applications by which access to the load cell and cable is restricted, an in-line tag identification module could 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 positioned in series with the load cell cable before it is actually plugged into the ESL instrument. It is also possible to use this technique in applications where different calibrations could be required on the same load cell. The ifegti may have a single load cell and instrument, but may change which calibration is auto-selected by simply changing the in-line cable adapter. Since each cable adapter features a different tag identification chip, the ESL instrument will associate an alternative calibration data set with each in-line adapter. This can be useful, for instance, when a precision 6-point linearization from the load cell is required in two different operating ranges of the identical load cell.
Given that the burden cell has been changed into a TEDS-Tag unit, it may be attached to the ESL Model 4215 smart strain gauge indicator or even a CellMite intelligent digital signal conditioner. The very first time that it is connected, a typical calibration procedure is conducted 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 tension load cell and matches it with its calibration data. Out of this point forward, the system is entirely plug-and-play.