GE MTS6-3-2-1-0

1. Configuration String Decoder 

The model MTS6-3-2-1-0 follows GE Multilin's legacy part numbering scheme for the MTS (Motor Thermal Sensor) family. Unlike typical product codes where suffixes indicate options, the MTS6-3-2-1-0 is a fixed-configuration, pre-assembled RTD input module designed to pair with GE's 469, 369, and 239 motor protection relays. Each digit in the sequence represents a hardware or firmware attribute:

Position	Digit	Meaning
MTS	-	Base product family: Motor Thermal Sensor
6	-	Number of RTD inputs: 6 channels
3	-	Input type: 3-wire Pt100 (platinum, 100Ω at 0°C)
2	-	Output type: 4–20 mA analog (isolated per channel)
1	-	Power supply: 24V DC (nominal, 18–36V range)
0	-	Enclosure: DIN rail mount, IP20, no display

What this means: The MTS6-3-2-1-0 is a standalone, 6-channel RTD signal conditioner that converts Pt100 resistance readings into proportional 4–20 mA signals for direct connection to a motor protection relay's analog inputs. It is not a relay or controller itself – it is a sensor interface module that extends the RTD capacity of relays with limited built-in channels (e.g., the 239 relay, which has only 4 internal RTD inputs).

2. Product Overview

The GE MTS6-3-2-1-0 is a precision, six-channel RTD (Resistance Temperature Detector) input module designed for motor stator winding and bearing temperature monitoring. Built to complement GE Multilin's motor protection relays, this module converts low-level resistance changes from Pt100 sensors into industry-standard 4–20 mA analog signals. Each channel is fully isolated from the others and from the power supply, preventing ground loops that can cause measurement errors in industrial environments. The MTS6-3-2-1-0 is typically mounted in the motor control center (MCC) or local junction box, close to the motor, to keep RTD lead lengths short and minimize noise pickup.

The module is passive from a control perspective – it requires no configuration software, no DIP switches, and no address assignment. It is a linear, calibrated device that outputs 4 mA at 0°C and 20 mA at 200°C (default scaling). This "set and forget" simplicity makes it ideal for legacy system upgrades and field retrofits where programming tools may not be available.

3. Key Features

• 6 independent Pt100 input channels – 3-wire connection (compensates for lead resistance)

• Linearized 4–20 mA output – 0°C to 200°C range (factory calibrated; other ranges available upon special order)

• Per-channel isolation – 1500 Vrms channel-to-channel and channel-to-power supply

• Lead resistance compensation – automatically cancels up to 25Ω per lead (approx. 250 feet of 24 AWG wire)

• Input protection – reverse polarity protection on RTD leads; 240V AC fault protection (transient)

• Output drive capability – each 4–20 mA output can drive up to 750Ω load (e.g., 24V loop with 500Ω relay input)

• LED status indicators – green (power OK), yellow (per-channel "active" – flashes when RTD is connected and within range)

• DIN rail mounting – standard 35mm EN 60715 rail, with snap-on clip

• No configuration required – 0–200°C fixed scaling simplifies installation

  
  

  
  

4. Technical Parameters 

RTD Inputs (Per Channel):

• Sensor type: Pt100 (α = 0.00385, IEC 60751)

• Connection: 3-wire (mandatory – 2-wire not supported)

• Input range: –50°C to +250°C (though output is calibrated 0–200°C; excursion outside 0–200°C saturates output)

• Lead resistance compensation: Up to 25Ω per lead (auto-canceling)

• Excitation current: 1 mA (constant current source, low self-heating)

• Input impedance: >10 MΩ (differential)

• RTD fault detection: Open-circuit detection (output goes to <3.5 mA or >21.5 mA depending on failure mode – fails low by default)

• Maximum RTD lead length: 300 meters (1000 feet) of 24 AWG twisted pair, shielded

Analog Outputs (Per Channel):

• Output type: 4–20 mA (current sink – requires external loop supply 12–36V DC)

• Scaling: 4 mA = 0°C, 20 mA = 200°C (linear)

• Output accuracy: ±0.25% of span (±0.5°C at 100°C) at 25°C ambient

• Temperature drift: ±0.02% of span per °C (max)

• Load capability: 0–750Ω (at 24V loop supply)

• Resolution: 12 bits (approximately 0.05°C per bit)

• Output update rate: 20 ms per channel (all channels updated sequentially)

Power Supply:

• Nominal voltage: 24V DC

• Operating range: 18–36V DC (including ripple)

• Current consumption: 120 mA at 24V DC (typical) – plus 20 mA per output loop if loops are powered from the same supply

• Power dissipation: <5W (full load)

• Reverse polarity protection: Yes (diode-protected)

Physical & Environmental:

Parameter	Value
Dimensions (H x W x D)	110 x 82 x 65 mm (4.33 x 3.23 x 2.56 in)
Weight	0.4 kg (0.88 lb)
Mounting	DIN rail 35mm (EN 60715)
Terminal type	Screw clamp (0.2–2.5 mm² / 24–14 AWG)
Enclosure rating	IP20 (for use inside control cabinet)
Operating temperature	–20°C to +60°C (–4°F to +140°F)
Storage temperature	–40°C to +85°C (–40°F to +185°F)
Humidity	5–95% non-condensing
Vibration resistance	1g @ 10–150 Hz (IEC 60068-2-6)

Certifications:

• CE (EN 61326-1, EN 61010-1)

• UL 508 (Industrial Control Equipment)

• CSA C22.2 No. 14

• RoHS 2011/65/EU

  
  

5. Operational Philosophy 

The MTS6-3-2-1-0 operates as a dedicated signal conditioner with no user-programmable elements. Understanding its internal operation helps in troubleshooting:

RTD Excitation: Each channel sources a precise 1 mA constant current through the Pt100 sensor. The voltage drop across the sensor (V = I × R) is measured differentially between the + and – leads. Meanwhile, a third lead (sense) carries no current but allows the module to measure the voltage drop in the current-carrying leads and subtract it – this is the principle of 3-wire compensation.

Linearization: The resistance of a Pt100 sensor is not perfectly linear (it follows the Callendar-Van Dusen equation). The MTS6 contains a hardware polynomial linearizer (or a microprocessor with a lookup table) that converts the measured resistance to a linear temperature value. The output current is then proportional to this linearized temperature.

Output Circuit: Each output is a current sink (NPN transistor) that pulls current from an external loop supply. The module controls the transistor's base drive to maintain I_out = 4 mA + (T × 0.08 mA/°C) for T between 0 and 200°C. If T < 0°C, output saturates at 3.8 mA typical (fails low). If T > 200°C or RTD open, output goes to 3.5 mA or below (user-configurable fail-safe option – default is fail low).

Why 3-wire only? The MTS6-3-2-1-0 does not support 2-wire RTDs because lead resistance cannot be compensated accurately. For 2-wire installations, a 4th wire must be added to convert to 3-wire, or an external compensation circuit must be used.

6. Application Fields

• Large induction motors (500–10,000 HP) – winding RTD monitoring in power plants and refineries

• Synchronous motors – field winding temperature monitoring (requires special RTD mounting)

• Hydroelectric generators – thrust bearing and guide bearing temperature monitoring

• Compressor motors (centrifugal and reciprocating) – discharge temperature monitoring (RTDs i