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Description and application


ST 485x and STD 485x converters are intended for converting the signal of Pt 1000/3850 resistance-type temperature sensing elements to the digital signal of RS 485 serial bus. The standard temperature range is -50 to 150°C. Communication inputs are protected to overvoltage. In case the module is placed as terminal on the line, a terminating resistor can be attached to the wiring by shorting the contacts (the switch SW placed next to terminals for communication lines connection). All settings are stored in EEPROM memory. The electronic module is equipped with the WATCHDOG circuit, which safeguards proper program functioning in the microprocessor. These converters can be utilised in any control system compatible with communication protocol ADAM 4000, ADVANTECH and ModBus RTU. Easy mounting of the converters is ensured by the unique “S head” design invented by SENSIT s.r.o. The converters are designed to be operated in a chemically non-aggressive environment. The converters are made in three basic variants:

1. ST 485A – with a simple ASCII communication protocol corresponds with ADAM 4000 modules by ADVANTECH company. Thus, standard drivers for ADAM modules can be used in various control programmes. For easier operation, the green LED indicates if power supply is on and the red LED indicates that the module is communicating. The SD 1x0 module is provided by the INIT shorting jumper on its printed circuit board. If it is shorted when power is switched on, the module communicates on 00 address with 9600 Bd transfer speed without checksum.

2. ST485B – the command structure corresponds with the ARION communication protocol, which is used among control systems by Amit company.

3. ST 485C – the command structure corresponds with the ModBus communication protocol.


  • EC Declaration of Conformity – in accordance with Act 22/1997 Coll. on technical requirements on products as amended.
  • Calibration – The final metrological inspection – comparison with standards or working instruments – is carried out for all the products. Continuity of the standards and working measuring instruments is ensured within the meaning of the Section 5 of Act no.505/1990 on metrology. The manufacturer offers a possibility to supply the sensors calibrated in SENSIT s.r.o.’s laboratory (according to requirements of the EN ISO/IEC 17025 standard) or in an Accredited laboratory.  


  • Specifications
  • Wiring diagram
  • Dimensional draft
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Converter type ST 485A
STD 485A
ST 485B
STD 485B
ST 485C
STD 485C
Input signal Pt 1000/3850
Power supply 10 to 35 V DC(unstabilized) 14 to 24 V AC
Power consumption max. 1000mW
Measuring range -50 to 150 °C
Communication properties communication via RS 485 maximum segment length is 1200 m, asynchronous transfer
transfer speed 1200, 2400, 4800, 9600, 19200 Bd transfer speed 9600, 19200, 38400, 57 600 Bd - DIP switch preset transfer speed 9600 Bd
optional transfer speeds 1200, 2400, 4800, 9600, 19200, 57600, 115200 Bd - DIP switch
256 modules / 1 serial port 63 modules / 1 serial port 247 modules / 1 serial port
protocol consistent with ADAM modules protocol ARION protocol ModBus 1 stop bit, without parity
Accuracy of electronics 0.05 %
Accuracy of sensing element ± 0.5 °C
Resolution 0.01 °C
Ingress protection IN 65 according to EN 60 529
Recommended wire cross section 0.14 to 1.5 mm^2
Material of the connection head POLYAMID
Working conditions ambient temperature: -30 to 70 °C
relative humidity: max. 85% (at the ambient temperature 25 °C)
atmoshperic pressure: 87 to 107 kPa
Mass 0.2 kg

Note: Manufacturer reserves the right to make changes in design and technical characteristics of the products. For actual information, please always contact your dealer.

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