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| DC to RTD Converter — CVRTD |
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| Model CVRTD emulates RTD resistance in proportion to standard DC signals. It is
uniquely designed to output desired resistance values by employing various combinations
of resistors connected in parallel (See Figure 1). The semiconductor MOSFET switches
used for switching resistor combinations have advantages compared to mechanical
relays which could have problems in stability with the increasing contact resistance
in aging and the mechanical life limit. At power failure, the CVRTD output becomes open. As an option when ordering, a specific resistance within 10 to 500 ohms can be specified as output in such cases. The CVRTD has two (A) terminals and two (B) terminals, which can cover 2-wire, 3-wire and 4-wire type connections. Pt 100 is the standard output, however, special RTD is available for the resistances within 15 to 400 ohms. The housing is the same as used for M-Unit Series. The plug-in base socket is included. The zero and span adjustments are accessible behind the front lid cover. |
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 Figure 1 CVRTD Circuit Diagram |
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| APPLICATION EXAMPLES • System Upgrading with Additional Recorder/Controller Basically, the CVRTD is used to drive an RTD input device with a DC signal. When upgrading an existing temperature recording system (a), 4-20 mAdc signal in proportion to the temperature is needed as input to the new host recorder or temperature controller. However, the user still wants to use the existing RTD input recorder for local recording. Then, the RTD signal is converted into 4-20 mAdc by the RTD Transmitter (model: M2RS) and then provided to the upgraded system and the existing recorder via the CVRTD (b). • Changing Temperature Sensor Type without Replacing the Receiving Instrument Old temperature recording system using an expensive or rare type of RTD (a) must sometimes be replaced. However, the user found that this temperature sensor is very expensive or difficult to find though the recorder itself is still usable. Then the RTD is replaced with a thermocouple, which is converted into 4-20 mAdc by the Thermocouple Transmitter (model: M2TS) and then provided to the old recorder via the CVRTD (c). |
| SPECIFICATIONS | |
| Input | 4-20 mA or 1-5 Vdc |
| Output | Pt 100 resistance (unipolor) or special RTD for 15-4000 ohms |
| Max. wattage | 0.07 W |
| Power input | AC or DC |
| Output resolution | max. 0.05 ohms |
| Accuracy | ±0.3% or 0.1ohms, whichever is greater. |
| Response time | max. 0.5 seconds (0-90 %) |
| Dielectric strength | 2000 Vac @1 minute (input to output to power to ground) |
