Selecting a Resistor Module

    We offer a variety of resistor modules with different features which make them attractive for different applications. As with most products resistor modules are designed with a number of constraints: 

    • Platform - we offer solutions in both the PXI and PCI formats
    • Number of channels - the greater the number channels the lower the cost per channel, but the range and/or resolution of each channel may be more restricted. 
    • Range - as the range of the module is extended it needs more components, reducing range restricts the number of applications that can be served by a channel
    • Resolution - increasing resolution requires more components, degrading resolution decreases make it harder to achieve the required resistance value harder
    • Speed - faster operation can help reduce test time and reduce the duration of transients as the resistor state is changed transient resistance values
    • Power handling - the greater the power the resistor channel has to handle the bigger the components used have to be. Dissipation of high powers may impact component stability
    • Minimum resistance value - The lower the minimum resistance value required the greater the errors caused by relay contact resistance and copper trace losses.
    • Accuracy - high accuracy requires the use of low loss paths, management of thermoelectric EMF's and the use of higher stability (and therefore more expensive) resistors
    • Calibration Port - a calibration port allows the user the check the resistor channel without having to disconnect the user connector form the UUT. It can be used to select any of the resistor channels and connect it to a DMM to do an accurate 4-terminal measurement. This can help improve accuracy in the measurements and be used as a calibration support tool. However, it takes space and reduces increases the cost of the module

    The Pickering range of resistor modules all use real resistors, they do not use current loads or other electronic means to control the resistance value. So they all behave in exactly the same way as a real resistor does.

    RTD Simulation

    The most common application for resistor modules is simulation of temperature dependent resistors. Information on how to simulate platinum based sensors can be found here, including a utility program for conversion from temperature to resistance.

    Pickering Interfaces Resistor Module Range

    The following is a summary of the range from Pickering, the text should help you chose the best model for your application:

    40-260

    High performance three channel resistor module designed for wide resistance range with very fine setting resolution. Software control is easy since it uses resistance calls (in ohms) rather than bit patterns. It includes a on a separate connector. 

    High performance three channel resistor module designed for wide resistance range with very fine setting resolution. Software control is easy since it uses resistance calls (in ohms) rather than bit patterns. It includes a Calibration Port on a separate connector.

    40-260D_functional.jpg

    40-261

    This two channel module is similar to 40-260 but has a much lower bottom end resitance value. The design is optimized for high performance applications requiring low as well high resistance settings. It supports a separate Calibration Port on its own connector to ensure the best performance and uses a resistance call to set its value.

    40-262

    This module is designed to provide a narrow resistance range with high channel count and very high performance levels. It is designed specifically for RTD simulation applications. It uses resistance calls which can easily be adapted by user to turn into temperature calls corresponding to the users RTD device, a specific example can be found here Platinum Temperature Sensors and a software utility here PRT Utility. The 40-262 supports a separate calibration port.

    40-265 (PXI) and 50-265 (PCI)

    Designed specifically for strain gauge simulation this module includes a bridge circuit and excitation system to allow it to emulate a strain gauge. The resistance control range is very small and has very fine control, permitting it emulate small strain levels. It supports a calibration port.

    40-297(PXI) and 50-297 (PCI)

    An excellent alternative to 40-295/290 where an accuracy specification is important but not requiring the accuracy of the precision range. The design uses EMR's. Control is by resistance calls to the module and the module works out the best setting to achieve that resistance by use of stored calibration information in the module. The resistors fitted to 40-297 have a low temperature coefficient which leads to an excellent accuracy and temperature stability.

    40-293 (PXI) and 50-293 (PCI)

    For applications requiring less performance the 40-293 offers a lower cost alternative based on EMR's and lower accuracy resistors than 40-297. In addition to offering 2 or 4 channels the design also optionally supports 8 SPDT relays which can be used for general purpose switching applications or used to insert additional components into the resistor chains.

    40-295 (PXI) and 50-295 (PCI)

    Provides a denser solution than 40-290 and is suited to applications were accuracy is not critical but speed of operation is. It uses relay patterns for control, for new system designs we recommend using 40-297 unless speed is critical - based on reed relays the 40-295 offers much faster operating speed than EMR solutions which may be important in real time applications. Reed relays tend to have a higher thermo-electric EMF than EMR's, see Importance of Thermoelectric EMF in resistor simulators, and a higher contact resistance in the relay which leads to a higher residual path resistance.

    40-294 (PXI) and 50-295 (PCI)

    For applications requiring less performance and reed relays the 40-294 offers a lower cost alternative based on EMR's and lower accuracy resistors. In addition to offering 2 or 4 channels the design also optionally supports 8 SPST relays which can be used for general purpose switching applications or used to insert additional components into the resistor chains.

    40-280

    The 40-280 provides the user with a set of relays that allows the simple provision of fixed resistor values. Each resistor can be set to open circuit, resistor selected or shorted out. Channels can be added in parallel so that a few different fixed values can be offered across two connections. This module is a good choice where you simply need to have a few fixed values rather than a variable resistor. The resistors can either be fitted by the user (standard configuration) or Pickering Interfaces can offer a facility to load the required resistors.

    40-290

    Provides a simple variable resistor based on the use of a binary chain of resistors controlled by reed relays. It is controlled using relay patterns to set the resistance value, but has no claimed overall accuracy. It is bested suited for low cost dense applications not requiring the best accuracy available.

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