Field service engineers require a number of load cells spanning the numerous ranges required to calibrate their customers’ systems. They might also require the assortment to conduct an array of force measurements for a particular testing application. The process begins when the engineer has to modify the load cell which is linked to his instrument before he can continue. If the new cell is linked to the instrument, the appropriate calibration factors have to be installed in the Force Transducer.
Avoiding user-error is really 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, or even worse, corrupting the current 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 appropriate calibration details are optimal.
What exactly 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 can be stored on the inside of a memory chip which is installed within a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a large number of detailed electronic data templates with a few degree of standardization. Even when using the data templates, it is really not guaranteed that different vendors of TEDS-compliant systems will interpret what data is put into the electronic templates in the same manner. More importantly, it is not apparent the calibration data that is needed within your application will likely be backed up by a certain vendor’s TEDS unit. You have to also be sure that you have a way to write the TEDS data in to the TEDS-compatible load cell, through a TEDS-compatible instrument which includes both TEDS-write and TEDS-read capabilities, or through the use of various other, likely computer based, TEDS data writing system.
For precision applications, including calibration systems, it also need to be noted that calibration data which is stored in the stress cell is the same regardless of what instrument is connected to it. Additional compensation for the Torque Sensor itself is not included. Matched systems where a field service calibration group might be attaching different load cells to several instruments can present a problem.
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 can 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 like field calibration services.
Using the TEDS-Tag system, a little and cheap electronic identification chip is positioned inside the cable that extends from the load cell or it may be mounted within the cell housing. This chip has a unique electronic serial number which can be read through the ESL Model 4215 or CellMite to identify the cell. The cell will then be attached to the unit along with a standard calibration procedure is performed. The instrument automatically stores the calibration data within the unit itself combined with the unique load cell identification number from your microchip. Whenever that cell is reconnected for the instrument, it automatically recognizes the cell and self-installs the correct calibration data. True plug-and-play operation is achieved. With this system the calibration data can automatically include compensation for that particular instrument so that high precision matched systems may be realized. Moreover, if the cell is moved to another instrument, that instrument will recall the calibration data that it has stored internally for your 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 very small, which makes it very easy to squeeze 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 connected to load cells via a DB9 connector with identical pin outs. The electronic identification chip will not hinder the cell’s signals. Pin 3 from the DS2401 is not used and may be cut off if desired. Simply connecting pins 1 and two through the DS2401 to pins 8 and 7, respectively, in the ESL DB9 connector will enable plug-and-play operation.
When you use off-the-shelf load cells, it is often useful to locate the DS2401 inside the hood in the cable. The cell features a permanently mounted cable that protrudes from the cell housing. At the end of the cable, strip back the insulation through 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 few dollars in parts along with a simple cable termination procedure, you have taken a standard load cell and transformed it in to a TEDS-Tag plug-and-play unit.
For applications by which accessibility load cell and cable is restricted, an in-line tag identification module can 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 the load cell cable before it is plugged into the Weight Sensor. It is additionally possible to make use of this technique in applications where different calibrations could be required on the same load cell. The user may mbssap just one 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 every in-line adapter. This can be useful, as an example, in case a precision 6-point linearization in the load cell is necessary by two different operating ranges of the same load cell.