The MTT MS3020 is a terminal block type CT transmitter that reads the AC current output of a current transformer, calculates its true RMS value, and converts it into a standard, isolated DC output. It accepts 0~1A AC or 0~5A AC at 50/60Hz, tolerating 120% of rated value continuously and 10× rated value for up to 3 seconds, with a maximum crest factor of 3.
Output is DC current (4~20mA, 0~20mA) or DC voltage (10mV to 10V range), so it can match what your PLC or DCS accepts. Zero and span are adjustable by ±2.5% of span via front-accessible trimmers, with accuracy better than ±0.25% of span at 10% input or above (at 25°C±5°C) and temperature coefficient of ±0.2% of span per 10°C change. Response time is 400ms max (0 to 90%), with CMRR of 100dB min.
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, weighing 90g for the main unit plus 5g for the shunt resistor.
| Input Current Range | 0-1A AC or 0-5A AC, 50/60Hz |
| Allowable Continuous Input | 120% of rated value |
| Allowable Instantaneous Input | 10× rated value (within 3 seconds) |
| Crest Factor | 3 max. |
| Output Signal | DC current (4-20mA, 0-20mA) or DC voltage (10mV to 10V range) |
| Zero / Span Adjustment | ±2.5% of span, front-accessible trimmers |
| Accuracy | Better than ±0.25% of span with at least 10% input (at 25°C±5°C) |
| Temperature Coefficient | ±0.2% of span per 10°C change |
| Response Time | 400ms max. (0 to 90%) |
| CMRR | 100dB min. |
| 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 (main unit), 5g (shunt resistor) |
| Operating Temperature | -5 to 55°C, 5-90% RH non-condensing |
| Storage Temperature | -10 to 60°C |
Frequently asked questions
What is the MS3020 used for?
It converts the AC current from a current transformer into a clean, isolated 4 to 20mA or voltage signal for motor current monitoring, load monitoring, or general AC current metering on a PLC or SCADA system.
Why does true RMS calculation matter for this application?
Current from VSD-driven motors and other switching loads is often not a clean sine wave. A transmitter that only measures average or peak current can give a reading that doesn’t match the motor’s actual heating effect or what a true RMS clamp meter would show.
What’s the difference between the MS3020 and the MS3021?
The MS3020 is built for current transformer (CT) inputs, while the MS3021 does the same true RMS calculation for potential transformer (PT), or voltage, inputs. Use the MS3020 for current monitoring and the MS3021 for voltage monitoring.
Does the MS3020 need a separate power supply?
Yes, it runs on 24V DC or 12V DC and is not loop-powered.
Download MTT MS3020 Terminal Block Type CT Transmitter (RMS Calculation) information here
Datasheet: MTT MS3020 Spec Sheet (PDF)
Manual: MTT MS3000 Series User’s Manual (PDF)
