Field service engineers require a number of load cells spanning the various ranges necessary to calibrate their customers’ systems. They may also need the assortment to conduct a variety of force measurements for a particular testing application. The challenge begins when the engineer has to modify the load cell that is linked to his instrument before he can continue. When the multi axis force sensor is linked to the instrument, the correct calibration factors have to be installed in the instrument.
Avoiding user-error is a major challenge with manual data entry or with requiring the engineer to select from a database of stored calibration parameters. Loading a bad parameters, or even worse, corrupting the present calibration data, can lead to erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the load cell being attached to it and self-installing the proper calibration information 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 for connecting transducers to microprocessors and instrumentation systems.
With TEDS technology, data may be stored within a memory chip that 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 many amount of standardization. Even when using the data templates, it is really not guaranteed that different vendors of TEDS-compliant systems will interpret what data goes into the electronic templates in a similar manner. Most importantly, it is not apparent the calibration data that is needed inside your application will likely be backed up by a particular vendor’s TEDS unit. You must also be sure that you have a way to write the TEDS data into the TEDS-compatible load cell, through a TEDS-compatible instrument which has both TEDS-write and TEDS-read capabilities, or through the use of a few other, likely computer based, TEDS data writing system.
For precision applications, such as calibration systems, it should also be noted that calibration data that is certainly kept in the stress cell is the same whatever instrument is linked to it. Additional compensation for your instrument itself is not included. Matched systems in which a field service calibration group may be attaching different load cells to different instruments can present an issue.
Electro Standards Laboratories (ESL) has evolved 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 will also be supported. This may be a critical advantage in precision applications including field calibration services.
With all the TEDS-Tag system, a small and cheap electronic identification chip is placed within the cable that extends from your load cell or it may be mounted in the cell housing. This chip contains a unique electronic serial number which can be read through the ESL Model 4215 or CellMite to distinguish the cell. The cell is then linked to the unit and a standard calibration procedure is conducted. The instrument automatically stores the calibration data within the unit itself combined with the load sensor identification number from the microchip. Whenever that cell is reconnected to the instrument, it automatically recognizes the cell and self-installs the appropriate calibration data. True plug-and-play operation is achieved. With this system the calibration data can automatically include compensation for that particular instrument to ensure that high precision matched systems may be realized. Moreover, when the cell is relocated to another instrument, that instrument will recall the calibration data which it has stored internally for that load cell. The ESL instruments can store multiple load cell calibration entries. In this manner, multiple load cells can form a matched calibration set with multiple instruments.
Any load cell can easily be made into a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is easily offered by distributors or from ESL. The chip is very small, rendering it easy to match a cable hood or cell housing.
Both ESL Model 4215 smart strain gauge indicator and the CellMite intelligent digital signal conditioner are attached to load cells using a DB9 connector with identical pin outs. The electronic identification chip fails to hinder the cell’s signals. Pin 3 of the DS2401 is not used and may be stop 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 using off-the-shelf load cells, it is usually convenient to locate the DS2401 within the hood from the cable. The cell features a permanently mounted cable that protrudes from the cell housing. At the conclusion 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 within the connector’s hood. For a few dollars in parts and a simple cable termination procedure, you may 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 may be simply constructed. A straight through in-line cable adapter can incorporate the DS2401 electronic tag chip. In this particular application, the cable adapter is really positioned in series using the load cell cable before it is actually 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 may 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 a different calibration data set with every in-line adapter. This might be useful, for instance, in case a precision 6-point linearization of the load cell is required in 2 different operating ranges of the identical load cell.
Now that the load cell has been converted to a TEDS-Tag unit, it can be attached to the ESL Model 4215 smart strain gauge indicator or perhaps a CellMite intelligent digital signal conditioner. The 1st time it is connected, a typical calibration procedure is conducted to initialize the cell’s calibration data in 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 existence of the force transducer and matches it featuring its calibration data. Out of this point forward, the system is totally plug-and-play.