Bridge, RTD, Thermocouple or Voltage Conditioner with Balanced Constant Current Excitation
The option HC10 on the 28124 card is designed to support a wide variety of DC or AC sensor measurements including RTD, bridge, thermocouple and voltage inputs. Other features of the 28124 card include programmable gain to x8192 with 0.02% resolution, programmable precision low-pass filters and three wideband or filtered outputs per channel.
Option HC10 adds a precision current source that is optimized for measurements of resistance temperature device (RTD) sensor measurements. The current source level is programmable from 0 to 1.02375 mA in 0.25 µA steps. Measurements may be made using two or four leads to the sensor depending on the desired accuracy. The current source utilizes Precisions’ Balanced Constant Current™ (BCC™) technology to significantly reduce noise and power-line hum when compared to traditional single-ended topologies. Traceable 0.01% resistors may be substituted for the RTD to precisely calibrate the signal conditioner.
For thermocouple measurements, a precise programmable DC input voltage substitution is supported to simulate the thermocouple output voltage for various temperature spans. The DC level may be set between 1 mV and 100 mV on a per-channel basis with 100 µV resolution. A third party isothermal block may be used for reference junction compensation and the thermocouple linearization may be performed during post processing in the data acquisition system.
For full bridge sensor measurements on load cells, pressure sensors, piezo-resistive accelerometers or strain gage bridges, programmable balanced bipolar constant voltage excitation is provided. Excitation is programmable from 0 to 20V in 5 mV steps. Three-step bipolar shunt of R1 or R2 is provided using precision resistors. In addition, relay contacts are used to connect the sensor internal cal resistor (if equipped) to + and – excitation. AC shunt cal injects a precision AC current source to evaluate the effect on the system frequency response from the bridge output impedance working into the input cable capacitance.