VT585 / Termocouple converter
The thermocouple is necessary for measuring low to cryogenic temperatures and high up to flame temperatures. Converter is used to connect thermocouple type K and convert the temperature data in a format of the monitoring system. Converters can be connected in a daisy chain at a distance up to 100 meters. This converter is connected at the end of 1-Wire chain or can be used with RJ9 splitter connected to a chain.
Description
VT585 is a thermocouple signal converter to a 1-wire interface based on the MAX31850 chip. The standard delivery uses a MAX31850K designed for operation with a K-type thermocouple (Chromel-Alumel). The VT585 also includes a power supply voltage regulator and a 1-wire bus level converter for matching the MAX31850 low voltage chip with a 5V bus.
The 1-wire interface transmitter provides the compensated thermocouple temperature, its internal temperature (cold junction temperature) and also detects the thermocouple disconnection or closure.
Specifications
| Power supply | external |
| Supply voltage | 5...12V |
| 1-wire data bus voltage | 5V |
| Maximum current flowing on the data bus | 4mA |
| Resistance to pull-up on the data bus in VT585 | 22K |
| Maximum number of VT585 converters per bus (depends on the bus length) | 8pcs |
| Thermocouple converter resolution | 14bit / 0.25°С |
Resolution of the internal temperature transducer | 12bit / 0.0625°С |
Internal temperature measurement error | ±2°С |
Measuring range and accuracy with K-type thermocouple
| Measured temperature (thermocouple) °C | Converter temperature (cold junction) °C | Error ± °C |
|---|---|---|
| -270 ... +1372 | -40 ... +125 | 6 |
| +700 ... +1372 | -20 ... +85 | 4 |
| -200 ... +700 | -20 ... +85 | 2 |
| -100 ... +100 | 0 ... +70 | 1 |
Excluding the error caused by the non-linearity of the thermocouple and the measurement error of the cold junction temperature
Connection
The thermocouple converter can be connected either to:
- the 1-wire interface of the master modules of the vutlan (In most cases this requires an extension "VT10 / 1-Wire board", VT900 and VT960 have 1-wire bus installed by default)
- to third-party equipment with the 1-wire interface (for example, to a PC with 1-wire interface)
The 1-Wire interface is connected with a 4-core cable using an RJ-11 connector and a thermocouple connection using a detachable screw terminal block with a step of 5.08mm terminal.
Picture: 1-Wire diagram (VT585. Description.)
K-type thermocouple connection:
- "+" Chromel is usually marked as yellow;
- "-"Alumel is usually marked as red;
Configuration:
There is a 4-position dip switch in the converter with which you can assign an individual number to the converter. This number does not affect the operation of the converter. It serves to facilitate the identification of converters operating on the same bus. The number given with the dip switch has nothing to do with the standard 1-Wire device identifier.
Switch position "on" = 0, "off" = 1
| 1 | 2 | 3 | 4 | # |
|---|---|---|---|---|
| on | on | on | on | 0 |
| off | on | on | on | 1 |
| on | off | on | on | 2 |
| . | . | . | . | ... |
| on | off | off | off | 14 |
| off | off | off | off | 15 |
Software
The vutlan master modules of models VT900, 335, 325 have built-in support for the VT585 converter.
Under linux OS, the operation of the MAX31850K converter is tested in the OWFS package.
Installation
Connection of K-type thermocouples: connect two wires:
- "+" Chromel is usually labeled as yellow;
- "-" Alumel usually labeled as red;
Developer notes: