Maxim at a Glance
At Maxim, we invent highly integrated solutions that make technology seamless. We channel our collective expertise to stretch the limits of technology, understand your needs, and help you get to market faster.
$2.4 billion (approx.) revenue in FY2012
$605 million revenue in Q3 FY2013
$4.33 billion in assets in Q3 FY2013
$1.57 billion in cash in Q3 FY2013
President and CEO
San Jose, CA, U.S.
1983. We celebrate our 30th anniversary in 2013.
Keywords: 4-20mA transducers, 4-20mA translator, 4 to 20mA converter, A/D, ADC, a to d, analog digital, analog to digital converters, convertor Related Parts
APPLICATION NOTE 823
Two ICs Convert 4-20mA Signal to 0-5V Output
Nov 27, 2001
Abstract: This design idea describes a simple circuit that converts a 4-20mA signal to a 0V to 5V analog voltage ideal for conversion to digital with an analog-to-digital converter (ADC). The 4mA level from the transducer produces a 0V output and the 20mA level produces a 5V output. A current sense amplifier generates this analog 0V to 5V output. In addition, the circuit provides a comparator output that can be used to detect a zero current condition.
In standard process-monitoring equipment, the outputs of 4-20mA transducers must be converted to signal voltages suitable for measurement by an A/D converter. Four milliamps in the loop is usually calibrated as zero for the quantity being monitored, and should therefore produce 0V at the ADC input. (Non-zero current enables the system to distinguish a broken loop from the zero-signal condition.)
The circuit in Figure 1 monitors loop current with a current-sense amplifier (IC1), and employs a comparator/reference/op-amp device (IC2) to generate a ground-referenced output that ranges from 0V at 4mA to 5V at the full-scale loop current (20mA). For the resistor values shown (R2-R6), IC1 produces an output at pin 8 of approximately 1.25V at 4mA, and 6.25V at 20mA. In turn, the IC2 op amp (configured as a unity-gain difference amplifier) generates an output range of 0.05V to 5.045V. The IC2 comparator can be used to monitor input voltage or flag a pre-set loop current.
Figure 1. This circuit derives a 0V-5V output from a 4-20mA current-loop signal, using a load resistor of only 10Ω .
The circuit performs well with 1% resistors. Monte Carlo analysis indicates a worst-case output error of 5% due to resistance mismatch alone, but the performance with unmatched components was better than 1% at full-scale. By compensating for the dominant error (about +50mV of offset error at zero and full-scale), the circuit demonstrated an accuracy of better than 1% across the operating range (i.e., from 4mA to 20mA).