The ProDAQ 5821 series of Signal Conditioning Cards is designed to interface with a variety of sensors, principally RTDs, Thermistors, Cryogenic Diodes and Voltage type sensors. Each version of the 5821 provides the capability of precise 4-wire measurement. In order to achieve this, a precise 500μA constant current source is provided per channel. The current source can be disabled on a per channel basis and is monitored to ensure that current is flowing. The value of the output current is stored on-board after calibration. In order to achieve the highest accuracy the output current may be automatically calibrated 'on-the-fly' using the ProDAQ 3416 24-bit Sigma-Delta ADC card and an on-board precision resistor.
The 5821-AA low cost version interfaces directly with the ProDAQ 3416. Typical accuracy achieved for a 4-wire PT-100 is 0.05°C and 0.003% for a 5kΩ thermistor.
The 5821-BA has per channel on-board gain and voltage calibration in order to achieve the highest accuracy possible. Typical accuracy for the 5821-BA for a PT-100 is 0.05°C and 0.002% for a 5kΩ thermistor. The 5821-BA also provides compensation for 3-wire sensors. With compensation employed the error on a 3-wire PT-100 can be reduced from several degrees to typically 0.1°C. The 5821-BA also provides support for 2-wire sensors so that the user need not make connections at the front panel of the SCU. This feature saves time when switching between different sensor types. The 5821-BA also includes broken wire detection as well as current monitoring.
The 5821-BB is similar to the 5821-BA but includes a second current source of 10μA, designed for use with cryogenic diodes. The 10μA current source is adjusted during calibration so that its typical absolute accuracy is 0.01%. The current source may also be used to make precision high resistance measurements, up to 1MΩ. Measurement accuracy at 1MΩ is typically 0.015%.