The MTT MS3705HA 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. Unlike a simple rotary-dial alarm setter, the MS3705HA shows the trip point on a bright 3-digit LED display and lets it be set in fine 0.1% steps, giving more precise and repeatable alarm thresholds along with a clear on-panel readout of exactly where each alarm is set.
Because the two relay outputs are electrically isolated from the input, from the power supply, and from each other, the MS3705HA can drive two independent alarm circuits, such as a low and a high limit, from a single measured signal, with adjustable hysteresis to prevent relay chatter near the trip point. Like the rest of the plug-in transmitter range, it clips into its own socket base so the unit can be swapped for calibration or replacement in seconds without disturbing the field wiring, and flexible AC or DC power plus wall or DIN rail mounting keep installation straightforward.
| Input | DC current (4-20mA standard; range 100μA-200mA) or DC voltage (0-10V standard; range 200mV-600V) |
| Input Resistance | 1MΩ minimum (voltage); 250Ω typical (current) |
| 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 selector switch, 0-105% of span in 0.1% steps |
| Setpoint Accuracy | Better than ±0.1% of span |
| Hysteresis | Adjustable 0.5-50.0% of span, ±0.1% of span accuracy |
| 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) |
| 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 |
| Response Time | 150ms maximum (0-90%) |
| Insulation Resistance | 100MΩ minimum at 500V DC |
| 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 |
| 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 MS3705HA 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 so you can read and set the alarm level directly on the unit.
How is the alarm set point adjusted?
Using a front-accessible selector switch, from 0-105% of the input span in fine 0.1% steps, with the value shown live on the 3-digit LED display.
What’s the difference between the MS3705HA and the standard MS3705?
The standard MS3705 sets its alarm point with a rotary switch and no display. The MS3705HA adds a 3-digit LED readout and finer 0.1% step adjustment for more precise, easily verified alarm thresholds.
What’s the difference between the MS3705HA and the MS3705HB?
Both are digital alarm setters in the same family; they differ in setpoint range or hysteresis behaviour. Tell us your process signal and the alarm trip levels you need, and we can confirm the right variant.
Can the MS3705HA replace an existing analogue alarm relay unit?
In most cases yes, as long as the input signal type and range match. Send us the model on the old unit’s label, or your input signal and the relay rating you need, and we’ll check compatibility before you order.
Download MTT MS3705HA Slim Plug-In Digital Alarm Setter information here
Spec Sheet: MTT MS3705HA Spec Sheet
Manual: MTT MS3705HA Manual
