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RC SYSTEMS
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ST-49 TOXIC/OXYGEN 2-WIRE 4-20mA SENSOR TRANSMITTER WITH FAULT SUPERVISION CIRCUITRY
- Field replaceable toxic / oxygen sensor module.
- Range & target gas configured on sensor module.
- Improves system noise immunity because low level sensor signals are protected within the grounded sensor head.
- Industry standard 4-20mA signal may be transmitted thousands of feet on 2-wires.
- CSA certified for Division 1 & 2 hazardous areas. May be installed as intrinsically safe device with a barrier, or, explosion-proof for NEMA 7 installations.
- Easily interfaced to R. C. Systems 1, 2, 6, or 16 channel receiver / display / alarm products.
- 2-wire 4-20mA signal is nonpolar with protective “steering diode” interface.
- Standard "Fault Supervision" circuitry continuously monitors for failed or missing sensor. 4-20mA output transmits <2mA during Fault condition.
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The R. C. Systems Co. Inc. Model ST-49 is a 2-wire 4-20mA Sensor Transmitter . It accepts low power toxic or oxygen electrochemical sensor modules and functions in a 2-wire 4-20mA “sink” mode to transmit gas values to an appropriate receiver device. The ST-49 overcomes noise immunity problems associated with electrochemical sensors by enclosing all low level signals within a grounded sensor head. Target gas type and range are determined by the field replaceable sensor module.
Calibration and / or validation of monitored gas values must be performed at the receiver device. R. C. Systems Inc. offers single, dual, six, eight and 16 channel receivers suitable for calibration, display, alarm and transmission of monitored gas values.
The ST-49 is enclosed in a rugged stainless steel enclosure with a flame arrestor suitable for installation into potentially hazardous environments. It has dual CSA certifications including intrinsically safe (IS) with an approved IS barrier, or explosion-proof in NEMA 7 installations. An optional junction box is available for connection to field wiring. A special ST-49IS model is available without the NEMA 7 stainless steel flame arrestor for use in ordinary or intrinsically safe only applications where stainless steel is reactive to the target gas (such as chlorine).
Missing or defective sensors are detected and flagged by transmitting a value of less than 2mA to the receiver. Sensor elements are interchangeable with other R. C. Systems Inc. “smart” sensor products to reduce spare sensor inventory requirements.
The ST-49 functions with loop voltages ranging from 9 - 30VDC. Voltage drop across the ST-49 is less than 9 volts. An integral “transient voltage suppressor” protects the ST-49 and receiver devices in case of lightning or other surge voltage levels.
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