The MTT MS3705HB is a slim plug-in digital alarm setter that watches a DC current or voltage signal and switches two independent, isolated relay outputs when the signal crosses a set point. It accepts a wide choice of current and voltage input ranges, and its trip point is shown on a bright 3-digit LED display and set in fine 0.1% steps on a front-accessible rotary switch, giving a precise, clearly readable alarm threshold rather than a plain dial with no feedback.
Selectable relay activation modes let the two outputs be configured to match how the alarm should behave relative to the set point and hysteresis band, and adjustable hysteresis prevents the relays from chattering when the signal sits near the trip point. Because the two relay outputs are isolated from the input, the power supply, and each other, the MS3705HB can drive two independent alarm circuits from a single measured signal. Like the rest of the plug-in transmitter range, it clips into its own socket base for fast calibration or replacement, and flexible AC or DC power plus wall or DIN rail mounting keep installation straightforward.
| Input | 4-20mA, 2-10mA, 1-5mA, 0-20mA, or 10-50mA DC current, or 0-1V to ±10V DC voltage (selectable) |
| Input Resistance | 250Ω (4-20mA), 100Ω (1-5mA), or 10Ω (10-50mA) |
| Allowable Input | 40mA DC max. continuous (current); 30V DC continuous (voltage) |
| Setpoint Display | Red LED, 3-digit, 8.0mm digit height |
| Setpoint Adjustment | Front-accessible rotary switch, 0-105% of span (0.1% steps up to 100%, 1% above) |
| Setpoint Accuracy | Better than ±0.1% of span |
| Hysteresis | Adjustable 0.5-50.0% of span, ±0.1% accuracy, via front switch |
| Relay Activation Modes | Four selectable modes controlling relay behavior relative to set point and hysteresis |
| Output | Two independent, isolated Form C relay contacts |
| Relay Rating | 5A at 125V AC or 5A at 30V DC (max. 250V AC / 30V DC, 5A NO / 3A NC) |
| Relay Electrical Life | 50,000 cycles (5A, 250V AC); 100,000 cycles (5A, 30V DC) |
| Response Time | 150ms maximum (0-90%) |
| Power Supply | 100-240V AC (7.0VA max), 24V DC (2.2W max), or 100-240V DC (8.4W max) |
| Accuracy | Better than ±0.1% of span |
| Temperature Effect | Better than ±0.15% of span per 10°C change |
| Power Sensitivity | Better than ±0.1% of span |
| Insulation Resistance | 100MΩ minimum at 500V DC |
| Dielectric Strength | 2000V AC for one minute |
| Relay Start-up Delay | 2 seconds standard; adjustable 1-60 seconds |
| Dimensions (W x H x D) | 29mm x 86mm x 125mm |
| Weight | Main unit 130g; socket 80g |
| Mounting | Wall or DIN rail mounting, plug-in socket base |
| Terminals | M3.5 screw terminals, 0.8-1.0Nm torque |
| Operating Temperature | -5 to 55°C ambient (storage: -10 to 60°C) |
| Operating Humidity | 5-90% RH, non-condensing |
Frequently Asked Questions
What is the MTT MS3705HB used for?
It monitors a DC current or voltage process signal and switches relay contacts when the signal crosses a set point, with the trip point shown on an LED display and selectable relay activation modes to match how the alarm should behave.
What input ranges does the MS3705HB accept?
A wide choice of DC current ranges (4-20mA, 2-10mA, 1-5mA, 0-20mA, or 10-50mA) or DC voltage up to ±10V, selectable to match your existing signal.
What’s the difference between the MS3705HB and the MS3705HA?
Both are digital alarm setters with an LED setpoint display. The MS3705HB adds a wider choice of selectable current/voltage input ranges and selectable relay activation modes, where the MS3705HA covers a simpler fixed input range.
What’s the difference between the MS3705HB and the standard MS3705?
The standard MS3705 sets its alarm point with a plain rotary switch and no display. The MS3705HB adds a 3-digit LED readout, fine 0.1% step adjustment, and selectable input ranges and relay modes.
How do I know which MS3705 variant I need?
Send us your process signal type and range, whether you need a digital display, and how you want the relays to behave relative to the set point, and we’ll confirm the right variant.
Download MTT MS3705HB Slim Plug-In Digital Alarm Setter information here
Spec Sheet: MTT MS3705HB Spec Sheet
Manual: MTT MS3705HB Manual
