4-20 mA Loop CalibratorRoy Matson

Notes 1) Small capacitor across regulator pins to prevent oscilation with some loads 2) Place 250 Ohm jumper across source terminls to give 1-5 VDC or 0-100 mV 3) Source and simulate modes both start at 4 mA 4) Use high quality fixed resistors with wire wound trim pots for accurate calibration 5) Optional 0-100 mV output at 4 mA for t/c, pH simulation, The pot can also be used to simulate RTDs

2 x 9 VoltBasic Circuit

LM-317Regulator

The LM-317 voltage regulator holds the voltage between Adj & Output pins at 1.25 Volts, therefore current is set by the value of resistor chain

In OutAdj

1.25 Volts

250 Ohm Jumper(for 1-5 V & mV)

2 x 9 VoltIn

AdjOut

312.5 Ohms

104 Ohms

156 Ohms

312.5 Ohms

625 Ohms

1250 Ohms

4 mA

+12 mANote 4

+8 mA

+4 mA

+2 mA

+1 mA

Tx. Simulate

Source

++ -

Batt Test

0.1 mF Note 1

1K 12 V

25 Ohms

1K 10 Turn

+mV Option

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Note 5