Field service engineers require a variety of load cells spanning the numerous ranges needed to calibrate their customers’ systems. They may also require the assortment to conduct a variety of force measurements for the testing application. The challenge begins once the engineer needs to modify the load cell which is connected to his instrument before he could continue. If the new cell is attached to the instrument, the correct calibration factors must be placed in the Force Sensor.
Avoiding user-error is really a major challenge with manual data entry or with requiring the engineer to pick from 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 attached to it and self-installing the appropriate calibration data 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 that include common, network-independent communication interfaces to connect transducers to microprocessors and instrumentation systems.
With TEDS technology, data can be stored inside of a memory chip which is installed inside of a TEDS-compliant load cell. The TEDS standard is complicated. It specifies a large number of detailed electronic data templates with some level of standardization. Even while using the data templates, it is not guaranteed that different vendors of TEDS-compliant systems will interpret what data goes into the electronic templates in a similar manner. More importantly, it is not apparent that this calibration data that is required inside your application is going to be backed up by a particular vendor’s TEDS unit. You must also be sure that you have a means to write the TEDS data into the TEDS-compatible load cell, through either a TEDS-compatible instrument that 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, like calibration systems, it should also be noted that calibration data that is saved in the burden cell is the same regardless of what instrument is linked to it. Additional compensation for your Torque Sensor is not included. Matched systems where a field service calibration group might be attaching different load cells to different instruments can present an issue.
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 could 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 can be a critical advantage in precision applications including field calibration services.
Using the TEDS-Tag system, a small and cheap electronic identification chip is positioned within the cable that extends through the load cell or it may be mounted inside the cell housing. This chip has a unique electronic serial number that can be read through the ESL Model 4215 or CellMite to identify the cell. The cell will be attached to the unit along with a standard calibration procedure is carried out. The instrument automatically stores the calibration data inside 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 appropriate 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 could be realized. Moreover, when the cell is transferred to another instrument, that instrument will recall the calibration data which it has stored internally for your 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 readily offered by distributors or from ESL. The chip is very small, which makes it easy to squeeze into a cable hood or cell housing.
Both the ESL Model 4215 smart strain gauge indicator and 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 hinder the cell’s signals. Pin 3 of the DS2401 is not really used and can be stop if desired. Simply connecting pins 1 and 2 from the DS2401 to pins 8 and 7, respectively, in the ESL DB9 connector will enable plug-and-play operation.
When using off-the-shelf load cells, it is usually useful to locate the DS2401 in the hood of the cable. The cell comes with a permanently mounted cable that protrudes from the cell housing. After 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 inside the connector’s hood. For a couple of 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 in which access to the 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 really put into series using the load cell cable before it is plugged into the Load Sensor. Additionally it is easy to utilize this technique in applications where different calibrations could be required on the same load cell. An individual may mbssap just one load cell and instrument, but could change which calibration is auto-selected by simply changing the in-line cable adapter. Since each cable adapter includes a different tag identification chip, the ESL instrument will associate an alternative calibration data set with each in-line adapter. This can be useful, as an example, in case a precision 6-point linearization in the load cell is required by two different operating ranges of the same load cell.