We had an enquiry from a customer replacing an old RTD temperature transmitter on a reactor vessel. The existing unit had failed, and they wanted a straightforward swap — but the new setup also needed the same temperature reading sent to both the local PLC and a separate data logger, and the old wiring only ran to one output.
This looks simple on paper — an RTD transmitter is an RTD transmitter — but a few things trip people up. Lead wire resistance on long cable runs adds error if the transmitter isn’t built to tolerate it. Not every RTD element is the same: Pt100, JPt100, Pt50, and Ni508.4Ω all have different resistance curves, and the wrong input type setting gives a reading that’s off by a wide margin. And feeding two separate downstream systems from one sensor means the two outputs need to be properly isolated from each other, or you risk ground loops and noisy readings on both sides.
For this, we would normally recommend the MTT MS3702, a slim plug-in RTD temperature transmitter. It accepts Pt100Ω, JPt100Ω, Pt50Ω, Ni508.4Ω, and other RTD types, and converts the resistance reading into a clean 4-20mA, 0-20mA, or configurable DC voltage output. It’s available as a single output or isolated dual output model — the dual version keeps Output 1 and Output 2 fully isolated from each other, from the input, and from the power supply, so one sensor can safely feed two separate systems without interference. It tolerates lead wire resistance up to 200Ω per wire, and mounts on its own DIN-rail plug-in socket base, so the unit itself can be swapped for calibration or replacement in seconds without touching the field wiring.
Before we quote, we would normally check:
- RTD element type (Pt100, JPt100, Pt50, Ni508.4Ω, or other)
- Whether you need a single output or isolated dual output
- Output signal range required (4-20mA, 0-20mA, or voltage)
- Power supply available at the panel (AC or DC)
- Approximate lead wire run length, if it’s a long cable
Hope this helps — send us your RTD type and the output signal you need, and we can confirm the right model.
| Input Types | Pt 100Ω, JPt 100Ω, Pt 50Ω, Ni 508.4Ω, or custom (range -200 to +850°C depending on type) |
| Minimum Input Span | 30-100°C depending on RTD type |
| Excitation Current | Approximately 1mA for Pt type at 0-100°C |
| Lead Wire Resistance | 200Ω maximum per wire |
| Output | 0-20mA DC, 4-20mA DC, or 10mV to 20V DC span range (single or isolated dual output) |
| Output Load (Current) | Single 4-20mA: max 750Ω; dual outputs: max 550Ω (Output 1), 350Ω (Output 2) |
| Isolation | 4-way isolation between input, output, power, and ground |
| Power Supply | 100-240V AC, 24V DC, or 100-240V DC (approx. 5.5-7.0VA AC or 1.6-1.8W DC) |
| Accuracy | Better than ±0.15% of span (at 25°C±5°C) |
| Temperature Effect | Better than ±0.2% of span per 10°C change |
| Response Time | 170ms maximum (0-90%) |
| CMRR | Minimum 100dB (500V AC, 50/60Hz) |
| Dimensions (W x H x D) | 29mm x 86mm x 125mm |
| Weight | Main unit 120g; socket 80g |
| Mounting | Wall or DIN rail mounting, plug-in socket base |
| Terminals | M3.5 screw terminals |
| Operating Temperature | -5 to 55°C ambient (storage: -10 to 60°C) |
| Operating Humidity | 5-90% RH, non-condensing |
| Standards | CE marked (EMC and Low Voltage Directives); Installation Category II, Pollution Degree 2 |
Frequently Asked Questions
What is the MTT MS3702 used for?
It converts an RTD (resistance temperature detector) signal into a standard 4-20mA, 0-20mA, or DC voltage output that a PLC, DCS, or panel meter can read directly.
Can the MS3702 be used with 2-wire, 3-wire, or 4-wire RTDs?
The MS3702 tolerates lead wire resistance up to 200Ω per wire. For the exact wiring configuration your sensor uses, we’d confirm the terminal connections against the manual before you order.
What’s the difference between the MS3702 and the MS3701 / MS3701F?
The MS3701 and MS3701F are thermocouple transmitters — they take a millivolt thermocouple input. The MS3702 is built for RTD (resistance) inputs instead. Match the transmitter to the sensor type you actually have.
What’s the difference between the MS3702, MS3702-01, and MS3702B?
These are variants within the same RTD transmitter family with different output or configuration options. If you’re replacing an existing unit, check the exact model code on the old unit’s label, or send us your input and output requirements and we’ll confirm the right variant.
How do I know which MS3702 model I need?
Check your RTD element type, whether you need single or dual isolated output, and the output signal your PLC or DCS expects. Send us these details and we can confirm the right model before you order.
Download MTT MS3702 Slim Plug-In RTD Temperature Transmitter information here
Spec Sheet: MTT MS3702 Spec Sheet
Manual: MTT MS3702 Manual
