EXP accessory items such as the EXP-16, EXP-16/A, EXP-800, EXP-1600 or EXP-1800 are most often used for two reasons:
- to increase the channel count of a plug-in board product
- to add CJC and high gain features required for thermocouple measurements
Each EXP accessory adds 16 channels to a system. These 16 channels are connected to one of the native channels of the DAS or KPCI plug-in board. The digital output lines of the DAS or KPCI board are used to control the address lines of the EXP accessory to determine which of the additional 16 channels of the EXP is feeding the native plug-in board channel.
Since switching of the digital output lines must be performed in concert with analog input sampling, overall throughput of the system can be compromised. The older DAS-1600 Series products would, for example, disable the use of DMA mode when EXP channels are enabled. Without DMA mode, upper limit of sampling speed would be limited to a few kilohertz.
Any upgrade or board replacement should be carefully planned. Often times software and cabling changes are required. Sufficient time should be allowed for complete understanding of the existing system as well as testing of the migrated system to fully discover any subtle differences. Study the documentation for your current system (or reverse engineer it from the wiring and source code) to determine which features of the products are actually in use by the application. Often, only a portion of the board's features are required, so board replacement purely on feature specifications can be misleading.
Upgrading to Instrument products: The Integra Series are multichannel digital multimeter/switch systems that can be controlled over RS-232, GPIB or Ethernet. The mainframes (Models 2700, 2701 or 2750) can perform as a digital multimeter and provide numerous measurement functions: DC volts, AC volts, 2wire Ohms, 4wire Ohms, Temperature based on T/C, RTD or Thermistor, and many more. The mainframes can accept switching modules to achieve a multichannel measurement system.
A typical configuration would be the 2700 with 7700 switch card to achieve a 20 channel system that has an internal CJC sensor for use with thermocouple sensors. Forty channel switch cards (7708) are also available as well as numerous others in the 77xx line. A model 2750 mainframe with all five slots populated with 7708 modules will yield a 200 channel system.
While reading rates of Instrument based products are typically slower than plug-in board products, the integrating A/D converters of instruments gives a much greater immunity to noise than plug-in board products. This greater noise immunity eliminates the need for signal averaging which is a common technique required when using plug-in board based systems. The effective sampling rates, especially for temperature monitoring systems, are quite comparable when considering that each single measurement from an instrument will be good data.
Upgrading to PCI cards: If wishing to continue to use your EXP accessories with PCI cards then the KPCI-3107 and KPCI-3108 can interface to EXP-16 or to EXP-1800 accessories. In both cases, a screw terminal panel is required for ease of connection (or you make a custom cable). The STA-3108-A2 provides a 37 pin D connector which will allow the EXP-16 to be connected. The STA-3108-A1 provides a 50-pin ribbon for the EXP-1800. When EXP accessories are used with PCI cards, the PG-408A DC to DC converter and an external 5VDC power supply is required.
However, it may be possible to stop using the EXP accessories all together. An option for high channel count and support of thermocouple measurements is the KPCI-1801HC with the STA-1800HC screw terminal board (CJC sensor). This board has 64 Single Ended channels and gains of 1, 5, 50 and 250. If the high gains for thermocouple signal amplification are not required, the KPCI-1802HC has gains of 1, 2, 4 or 8 for use with more general purpose measurements.
Other high channel count options in PCI form factor are the KPCI-3110 or KPCI-3116. Both these boards have 32 Single Ended channels at gains of 1, 2, 4 or 8. The KPCI-3116 is a 16bit board rated for 200KHz sampling rate; the KPCI-3110 is a 12bit board rated for 1MHz sampling rate.