Field service engineers require many different load cells spanning the numerous ranges required to calibrate their customers’ systems. They could also require the assortment to conduct an array of force measurements for the testing application. The task begins when the engineer needs to alter the load cell which is connected to his instrument before he could continue. When the new cell is attached to the instrument, the correct calibration factors have to be installed in the Force Transducer.
Avoiding user-error is a major challenge with manual data entry or with requiring the engineer to pick from a database of stored calibration parameters. Loading the incorrect parameters, as well as worse, corrupting the current calibration data, can lead to erroneous results and costly recalibration expenses. Instrumentation that automatically identifies the stress cell being connected to it and self-installing the proper calibration data is 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 including common, network-independent communication interfaces for connecting transducers to microprocessors and instrumentation systems.
With TEDS technology, data can be stored within a memory chip which is installed inside of a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a huge number of detailed electronic data templates with a few level 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. Moreover, it is not apparent that this calibration data that is needed inside 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 method to write the TEDS data in to the TEDS-compatible load cell, either through a TEDS-compatible instrument which has both TEDS-write and TEDS-read capabilities, or with the use of various other, likely computer based, TEDS data writing system.
For precision applications, like calibration systems, it should also be noted that calibration data which is kept in the load cell is identical no matter what instrument is attached to it. Additional compensation for the Rotary Torque Sensor is not included. Matched systems where a field service calibration group may be attaching different load cells to different 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 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 will also be supported. This may be a critical advantage in precision applications including field calibration services.
With all the TEDS-Tag system, a little and inexpensive electronic identification chip is placed inside the cable that extends from the load cell or it may be mounted inside the cell housing. This chip includes a unique electronic serial number that can be read through the ESL Model 4215 or CellMite to distinguish the cell. The cell will then be linked to the unit as well as a standard calibration procedure is conducted. The instrument automatically stores the calibration data within the unit itself along with the unique load cell identification number from 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. Using this system the calibration data can automatically include compensation for your particular instrument so that high precision matched systems could be realized. Moreover, in the event the cell is relocated to another instrument, that instrument will recall the calibration data which it has stored internally for the 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 easily be made right 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 quite small, which makes it very easy to squeeze into a cable hood or cell housing.
Both the ESL Model 4215 smart strain gauge indicator as well as the CellMite intelligent digital signal conditioner are attached to load cells by way of a DB9 connector with identical pin outs. The electronic identification chip does not interfere with the cell’s signals. Pin 3 in the DS2401 is not used and will be cut off if desired. Simply connecting pins 1 and 2 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 convenient 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 conclusion of the cable, strip back the insulation from your 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 couple 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 where accessibility 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. Within this application, the cable adapter is actually placed in series using the load cell cable before it is actually plugged into the Load Cell. It is also possible to use this technique in applications where different calibrations might be required on the same load cell. The consumer may mbssap a single load cell and instrument, but could 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, as an example, in case a precision 6-point linearization in the load cell is needed in two different operating ranges of the same load cell.