We had an enquiry from a customer at a coastal processing plant whose control panels ran on a 24V AC transformer supply, not the usual mains AC or 24V DC. Their existing signal conditioners were also showing corrosion on the terminal contacts after a couple of years, which isn’t surprising given the humid, salt-laden air at the site.
Two separate things needed solving here. First, most signal conditioners are built for mains AC or DC power, so a 24V AC control transformer supply doesn’t always have a direct match. Second, a standard unit’s board and contacts aren’t necessarily built to shrug off a humid or corrosive atmosphere over the long run — and once contacts start corroding, contact resistance creeps up and readings start drifting before anything visibly fails.
For this, we would normally recommend the MTT MS3704-S, a slim plug-in high-level signal conditioner built specifically to run from a 24V AC supply. It accepts the same range of DC current and voltage inputs as the standard MS3704 and converts them into a clean, isolated single or dual DC output. What sets it apart is conformal-coated construction and gold-plated contacts, which hold up much better in humid or corrosive environments than standard tin-plated terminals. Like the rest of the plug-in range, it mounts on its own DIN-rail socket base for fast swap-out.
Before we quote, we would normally check:
- Confirm 24V AC is the actual supply available (not 24V DC)
- Exact input signal type and range (current or voltage)
- Whether you need a single output or isolated dual output
- Ambient conditions at the panel (humidity, salt exposure, or corrosive gases)
Hope this helps — send us your supply voltage and site conditions, and we can confirm the right model.
| Power Supply | 24V AC ±15% (47-63Hz), approx. 2.0VA max (single output) or 2.5VA max (dual output); 160mA fuse |
| Input Types | DC current (100μA to 200mA) or DC voltage (200mV to 600V); common ranges include 4-20mA, 0-20mA, 0-10V, ±10V |
| Input Resistance | 100Ω to 1MΩ minimum, depending on signal type |
| Allowable Input Voltage | 30V DC max. continuous |
| Output | 0-20mA DC or -10V to +10V DC (single or isolated dual output) |
| Zero & Span Adjustment | Approximately ±5% of span |
| Isolation | 4-way isolation between input, output, power, and ground |
| Accuracy | Better than ±0.1% of span (at 25°C±5°C) |
| Response Time | 85ms maximum (0-90%); 10ms with /K fast-response option |
| Temperature Effect | Better than ±0.2% of span per 10°C change |
| CMRR | Minimum 100dB (500V AC, 50/60Hz) |
| Insulation Resistance | 100MΩ minimum at 500V DC |
| Dimensions (W x H x D) | 29mm x 86mm x 125mm |
| Weight | Main unit up to 120g; socket up to 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 |
| Construction | Flame-resistant resin housing (UL 94); gold-plated brass contacts with polyurethane anti-humidity coating |
Frequently Asked Questions
What is the MTT MS3704-S used for?
It’s a signal conditioner and isolator for DC current or voltage signals, powered from a 24V AC supply, built with conformal coating and gold-plated contacts for humid or corrosive sites.
What’s the difference between the MS3704-S and the standard MS3704?
They condition the same range of input signals, but the MS3704-S runs on 24V AC specifically (not mains AC/DC like the standard MS3704), and adds conformal coating and gold-plated contacts for better resistance to humidity and corrosion.
Is the MS3704-S suitable for coastal or high-humidity sites?
Yes — that’s the main reason for its construction. If your site has salt air, high humidity, or corrosive gases, the MS3704-S is generally a better fit than the standard model.
Can the MS3704-S run on 24V DC instead of 24V AC?
No — it’s built specifically for 24V AC power. If your panel supply is 24V DC, the standard MS3704 or the MS3704-D1 would be the right choice instead.
How do I know which MS3704 model I need?
Tell us your actual supply voltage type (AC or DC), your input signal, and your site’s ambient conditions. We’ll confirm the right model before you order.
Download MTT MS3704-S Slim Plug-In High-Level Signal Conditioner information here
Spec Sheet: MTT MS3704-S Spec Sheet
Manual: MTT MS3704-S Manual
