We had an enquiry from a customer who needed to isolate a single 4 to 20mA loop between a transmitter and their PLC, but the panel had no spare 24V DC terminals left for an extra device.
This looks simple, but most signal isolators need their own separate 24V or 12V DC power supply to operate, and finding a spare, properly fused terminal for that in an already-crowded panel isn’t always straightforward. If you skip isolation because of this, you’re left exposed to exactly the ground loop and noise problems that isolation is meant to solve.
For this, we would normally recommend the MTT MS3064, a terminal block type loop-powered isolator. It draws all the power it needs from the 4 to 20mA loop itself, so there’s no external power supply to wire in — you simply insert it in line with the existing current signal. It breaks the loop electrically into two isolated sections, eliminating ground loops and blocking common-mode noise between the transmitter side and the receiving instrument side. The compact, lightweight DIN-rail housing keeps the footprint small even in a crowded panel.
Before we quote, we would normally check the transmitter’s available loop voltage headroom, since a loop-powered isolator does add a small voltage drop to the loop, and the output signal type your PLC or recorder expects. Hope this helps — send us your loop details and we can confirm it will work.
| Input Signal | 4-20mA DC |
| Maximum Allowable Input Current | 30mA DC max. |
| Output Signal | 4-20mA DC or 1-5V DC |
| Maximum Load | 50kΩ min. (voltage output), 350Ω max. (current output, 50-350Ω range) |
| Accuracy | Better than ±0.1% of span |
| Temperature Coefficient | Better than ±0.15% per 10°C change |
| Response Time | 15ms max. (0 to 90%) |
| CMRR | 100dB min. (500V AC, 50/60Hz) |
| Isolation | 2-way isolation between input and output (loop-powered, no external supply needed) |
| Insulation Resistance | 100MΩ min. (@ 500V DC) |
| Dielectric Strength | 1500V AC for 1 minute |
| Enclosure / Mounting | DIN rail mounting, M3.5 screw terminal |
| Dimensions | W25.0 × H94.0 × D40.0 mm |
| Weight | 70g max. |
| Operating Temperature | -5 to 55°C, 5-90% RH non-condensing |
| Storage Temperature | -10 to 60°C |
Frequently asked questions
What is the MS3064 used for?
It isolates a single 4 to 20mA loop between a transmitter and a PLC or recorder, eliminating ground loops and blocking common-mode noise, without needing its own power supply.
Does the MS3064 need a separate power supply?
No, that’s what makes it different from most other isolators in this series. It draws all the power it needs from the current loop itself, so there are no power terminals to wire in.
Does adding the MS3064 affect the loop’s voltage budget?
Yes, like any loop-powered device it adds a small voltage drop to the loop, so it’s worth checking your transmitter’s available voltage headroom before adding it, especially on loops that are already running close to their limit.
Can the MS3064 output a voltage signal instead of 4 to 20mA?
Yes, the output can be configured as 4 to 20mA current or 1 to 5V voltage, depending on what your receiving instrument needs.
Download MTT MS3064 Terminal Block Type Loop-Powered Isolator information here
Datasheet: MTT MS3064 Spec Sheet (PDF)
Manual: MTT MS3000 Series User’s Manual (PDF)
