The MTT MS3120 is a terminal block type CT transmitter with two independent, isolated outputs. It reads the AC current output of a current transformer, calculates its true RMS value, and converts it into two separate standard DC signals. 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 1 and output 2 are independently configurable to current (0~20mA, 4~20mA) or voltage (0~10mV to ±10V ranges) – useful when one signal needs to feed a PLC and a second, separate signal needs to feed a recorder or indicator at the same time. 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 5-way isolation between input, output 1, output 2, power, and ground, with dielectric strength of 2000V AC (input/outputs) and 500V AC (between outputs), and insulation resistance of 100MΩ min at 500V DC.
Power supply is flexible: 100-240V AC, 24V DC (±10%), or 110V DC, drawing 6.5VA (AC), 1.6W (24V DC), or 2.5W (110V DC). The unit mounts on DIN rail with M3.5 screw terminals, in an ABS resin (UL 94V-0) enclosure measuring W49.8 × H102.0 × D40.0mm, weighing 140g 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 1 & 2 | Current (0-20mA, 4-20mA) or voltage (0-10mV to ±10V ranges), independently configurable |
| 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 | 100-240V AC, 24V DC (±10%), or 110V DC |
| Power Consumption | 6.5VA (AC), 1.6W (24V DC), 2.5W (110V DC) |
| Isolation | 5-way isolation between input, output 1, output 2, power, and ground |
| Insulation Resistance | 100MΩ min. (@ 500V DC) |
| Dielectric Strength | 2000V AC input/outputs; 500V AC between outputs |
| Enclosure / Mounting | ABS resin (UL 94V-0), DIN rail mounting, M3.5 screw terminal |
| Dimensions | W49.8 × H102.0 × D40.0 mm |
| Weight | 140g (main unit), 5g (shunt resistor) |
| Operating Temperature | -5 to 55°C, 5-90% RH non-condensing |
| Storage Temperature | -10 to 60°C |
| Standards | EMC Directive 2014/30/EU, Low Voltage Directive 2014/35/EU, Installation Category II |
Frequently Asked Questions
What is the MS3120 used for?
It reads AC current from a current transformer, calculates its true RMS value, and converts it into two independent, isolated DC outputs, so one current reading can feed two separate systems — for example a monitoring panel and a protection relay.
Can the MS3120 be used with AC power instead of 24V DC?
Yes. The MS3120 accepts 100-240V AC, 24V DC, or 110V DC, so it can be powered directly from panels that don’t have a dedicated 24V DC supply.
What’s the difference between the MS3120 and the MS3020?
The MS3120 gives two independent isolated outputs from one CT input and can run on AC or DC power. The MS3020 is a single-output transmitter powered only by 24V or 12V DC. Choose the MS3120 when the same current reading needs to feed two separate devices, or when only AC mains power is available at the panel.
Does the MS3120 work correctly on non-sinusoidal current from a VFD-driven load?
Yes. The MS3120 calculates true RMS, not just average current, so it stays accurate on distorted waveforms from variable-frequency drives and similar non-linear loads.
Download MTT MS3120 Terminal Block Type CT Transmitter information here
Datasheet: MTT_SpecSheet_MS3120_Rev210_E
Manual: MTT_Manual_MS3120_Rev170_E
