Field service engineers require a variety of load cells spanning the different ranges needed to calibrate their customers’ systems. They may also need the assortment to conduct a wide range of force measurements for a particular testing application. The challenge begins when the engineer must alter the load cell which is connected to his instrument before he can continue. When the multi axis force sensor is attached to the instrument, the proper 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 stress cell being mounted on 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 could be stored within a memory chip that is installed within a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a large number of detailed electronic data templates with some amount of standardization. Even while 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. Moreover, it is far from apparent that the calibration data that is needed in your application will likely be backed up by a specific vendor’s TEDS unit. You have to also be sure that you have a method to write the TEDS data to the TEDS-compatible load cell, through a TEDS-compatible instrument which 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, like calibration systems, it also need to be noted that calibration data that is certainly kept in the stress cell is the same whatever instrument is attached to it. Additional compensation for the instrument itself is not included. Matched systems where a field service calibration group could be attaching different load cells to various 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 can 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 to the user. Multiple load-cell and multiple instrument matched pair calibrations are also supported. This may be a critical advantage in precision applications like field calibration services.
With all the TEDS-Tag system, a tiny and cheap electronic identification chip is positioned within the cable that extends from the load cell or it can be mounted within the cell housing. This chip contains a unique electronic serial number that may be read from the ESL Model 4215 or CellMite to identify the cell. The cell is then attached to the unit along with a standard calibration procedure is performed. The instrument automatically stores the calibration data in the unit itself combined with the load sensor identification number from 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 so that high precision matched systems could be realized. Moreover, if the cell is moved to another instrument, that instrument will recall the calibration data it has stored internally for the 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 be simply made right into a TEDS-Tag cell. The electronic identification chip, Dallas Semiconductor part number DS2401, is easily provided by distributors or from ESL. The chip is quite small, making it very 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 via a DB9 connector with identical pin outs. The electronic identification chip does not affect the cell’s signals. Pin 3 from the DS2401 is not really used and will be cut off if desired. Simply connecting pins 1 and two from the DS2401 to pins 8 and 7, respectively, of the ESL DB9 connector will enable plug-and-play operation.
When you use off-the-shelf load cells, it is usually convenient to locate the DS2401 in the hood from the cable. The cell includes a permanently mounted cable that protrudes from the cell housing. After the cable, strip back the insulation from the individual wires and solder the wires into the DB9 connector. The DS2401 is soldered across DB9 pins 7 and 8, and fits in the connector’s hood. For a couple of dollars in parts as well as a simple cable termination procedure, you might have taken a standard load cell and transformed it in to a TEDS-Tag plug-and-play unit.
For applications where 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 particular application, the cable adapter is in fact positioned in series with all the load cell cable before it is actually connected to the ESL instrument. It is additionally easy to use this technique in applications where different calibrations could be required on the same load cell. The ifegti could have a single load cell and instrument, but can change which calibration is auto-selected by just 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 each in-line adapter. This can be useful, for instance, when a precision 6-point linearization from the load cell is necessary by two different operating ranges of the same load cell.
Since the load cell has been converted to a TEDS-Tag unit, it may be attached to the ESL Model 4215 smart strain gauge indicator or perhaps a CellMite intelligent digital signal conditioner. The very first time it is connected, a standard calibration procedure is conducted to initialize the cell’s calibration data in the instrument. The ESL instruments support many different 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. Using this point forward, the device is entirely plug-and-play.