The MTT MS3021 is a terminal block type PT transmitter that reads an AC voltage input, calculates its true RMS value, and converts it into a standard, isolated DC output. It accepts 0~110V AC, 0~150V AC, or 0~300V AC at 50/60Hz, with input resistance of 1MΩ min, tolerating 120% of rated input continuously and 1.5× rated input for up to 5 seconds, with a maximum crest factor of 3.
Output is 4~20mA DC, 0~20mA DC, or a voltage range from 10mV to 10V DC (including bipolar ranges), so it can match what your PLC or DCS accepts. Accuracy is better than ±0.25% of span at 10% input or above (at 25°C±5°C), with temperature effect better than ±0.2% of span per 10°C change. Response time is 400ms max (0 to 90%), with CMRR of 100dB min (500V AC, 50/60Hz).
There is 3-way isolation between input, output, and power, with insulation resistance of 100MΩ min at 500V DC and dielectric strength of 1500V AC for 1 minute.
Power supply is 24V DC (±10%) or 12V DC (±20%), drawing up to 50mA (24V) or 70mA (12V). The unit mounts on DIN rail with M3.5 screw terminals, in an ABS resin (UL 94V-0) enclosure measuring W25.0 × H94.0 × D40.0mm and weighing under 90g.
| Input Voltage Ranges | 0-110V AC, 0-150V AC, or 0-300V AC, 50/60Hz |
| Input Resistance | 1MΩ min. |
| Allowable Input (Continuous) | 120% of rated input value |
| Allowable Input (Instantaneous) | 1.5× rated input value (within 5 seconds) |
| Crest Factor | 3 max. |
| Output Signal | 4-20mA DC, 0-20mA DC, or voltage 10mV to 10V DC (incl. ± ranges) |
| Accuracy | Better than ±0.25% of span with at least 10% input (at 25°C±5°C) |
| Temperature Effect | Better than ±0.2% of span per 10°C change |
| Response Time | 400ms max. (0 to 90%) |
| CMRR | 100dB min. (500V AC, 50/60Hz) |
| Power Supply | 24V DC (±10%) or 12V DC (±20%) |
| Power Consumption | 50mA max. (24V current out), 70mA max. (12V current out) |
| Isolation | 3-way isolation between input, output, and power |
| Insulation Resistance | 100MΩ min. (@ 500V DC) |
| Dielectric Strength | 1500V AC for 1 minute |
| Enclosure / Mounting | ABS resin (UL 94V-0), DIN rail mounting, M3.5 screw terminal |
| Dimensions | W25.0 × H94.0 × D40.0 mm |
| Weight | 90g max. |
| Operating Temperature | -5 to 55°C, 5-90% RH non-condensing |
| Storage Temperature | -10 to 60°C |
| Standards | EMC Directive 2014/30/EU, EN61326-1:2013; Low Voltage Directive 2014/35/EU, IEC/EN61010-1:2010 |
Frequently asked questions
What is the MS3021 used for?
It converts the AC voltage from a potential transformer into a clean, isolated 4 to 20mA or voltage signal for bus voltage monitoring, supply voltage checks, or general power quality monitoring on a PLC or SCADA system.
Why does true RMS calculation matter for this application?
Voltage waveforms in plants with VSDs, UPS systems, or other power electronics are often distorted rather than a clean sine wave. A transmitter that only measures average or peak voltage can give a reading that doesn’t match a true RMS meter, which can throw off your alarm thresholds.
What’s the difference between the MS3021 and the MS3020?
The MS3021 is built for potential transformer (PT), or voltage, inputs, while the MS3020 does the same true RMS calculation for current transformer (CT) inputs. Use the MS3021 for voltage monitoring and the MS3020 for current monitoring.
Does the MS3021 need a separate power supply?
Yes, it runs on 24V DC or 12V DC and is not loop-powered.
Download MTT MS3021 Terminal Block Type PT Transmitter (RMS Calculation) information here
Datasheet: MTT MS3021 Spec Sheet (PDF)
Manual: MTT MS3000 Series User’s Manual (PDF)
