Precision 4-20 ma Current Loop Transmitter. Electronics Cookbook by Smart&Small online business park.


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Precision 4-20 ma Current Loop Transmitter.

Circuit designed to transmit analog 4-20 mA signals over an current loop. It provides accurate current scaling and output current limit functions. Microcontroller converted output voltage from a sensor to a PWM signal, and PWM converted to a proportional current, in which 4 mA represents the sensor’s zero-level, and 20 mA represents the full-scale level output.

Up to 12 bit PWM.

Low total error with PWM freq 1...4 kHz: < 0.1 %.

The cheapest solution for galvanic isolation precision current loop.

Wide operating temperature range: –40°C to +85°C.

Schematic diagram. Click to enlarge.

PCAD2006 Schematic file. Click to download.

Part Description Qty.

C1 0.1 uF ceramic capacitor 1

C2, C3 10 uF ceramic capacitor 2

C4, C5 0.1 uF ceramic capacitor 2

C6, C7 10 uF ceramic capacitor 2

C8 0.1 uF ceramic capacitor 1

D1 ADuM1100 digital isolator (Datasheet) 1

D2 XTR116 4-20mA Current Loop transmitter (Datasheet) 1

R1, R@ 10 kOhm 0805 resistors 2

VT1 BCX56 transistor (Datasheet) 1

U1 PSD0515 5 V to 15 V DC/DC converter 1

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