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Thermocouple Input Field Configurable Limit Alarm
TRODEKS Engineering | Thermocouples, Pressure Transducers, Flow Meters, PID Controllers
  • Provides Relay Contact Closures at a Preset Temperature Input Level
  • Field Configurable Input Ranges for Type J, K, T, E, R, and S Thermocouples
  • Dynamic Deadband Prevents False Trips
  • Burnout Detection
  • Setpoints Programmable HI or LO
  • Selectable Failsafe/Latching Operation
  • Selectable 120/240 Vac Input Power
 Manuals (contact with email : [email protected])


Model SMLA-TC of field configurable limit alarms with thermocouple input offers wide ranging inputs and flexiblesetpoint capability. It accepts six popular thermocoupletypes with inputs ranging from -270°C (454°F)to 1760°C (3200°F). The SMLA-TC provides twoindependent setpoint alarms (2 SPDT, 5A) andincludes 0.25% to 50% adjustable deadbands andselectable 120/240 Vac power.

Model SMLA-TC is equipped with a dual functiondiagnostic LED. The green center LED indicates linepower and input signal status. Active line power isindicated by an illuminated LED. If the center LED isoff, check line power and the wiring connection. If theinput signal is above 100% full scale, the LED will flashat approximately 8 Hz. Below 0%, the flash rate isapproximately 4 Hz.

Setpoints are top accessed multi-turn potentiometers.The field configurable SMLA-TC limit alarm setpointscan be configured for HI, LO, latching or fail-safetrip operation. Non-latching HI and LO setpointshave respective HI and LO deadbands. In a trippedcondition, the setpoint is exceeded and the appropriatered LED is lit. The trip will reset only when the processfalls below the HI deadband or rises above the LOdeadband. To reset a latched setpoint the signal mustbe in the safe region and the line power must beturned off for at least 5 seconds. For proper deadbandoperation, the HI setpoint must always be set above theLO setpoint.

In failsafe operation, the relay is energized when theprocess is below a HI setpoint or above a LO setpoint(opposite for non-failsafe). In the failsafe mode, a powerfailure results in an alarm condition.

The input must remain beyond the setpoint for100 milliseconds, uninterrupted, to qualify as a validtrip condition. Likewise, the input must fall outsidethe deadband and remain there for 100 millisecondsto return the alarm to an untripped condition. Thiseffectively results in a “dynamic deadband” - based ontime - in addition to the normal deadband.

The factory default configuration for the SMLA-TCis as follows:
Input: Type J, 0 to 360°C (32 to 680°F)
Burn Out: Positive
Output: Dual, SPDT
Trip: A: HI, B: LO
Latching: No
Failsafe: No
Deadband: A/B: 0.25%
Power: 120 Vac

When switching inductive loads, maximum relay life andtransient EMI suppression is achieved using externalprotection. Place all protection devices directly acrossthe load and minimize lead lengths. For AC inductiveloads, place a properly rated MOV across the load inparallel with a series RC snubber. Use a 0.01 to 0.1 mFpulse film capacitor (foil polypropylene recommended)of sufficient voltage, and a 47 Ω, ½ W carbon resistor.For DC inductive loads, place a diode across the load(PRV > DC supply, 1N4006 recommended) with (+) tocathode and (-) to anode (the RC snubber is an optionalenhancement).

Ranges: Field configurable, see table
Impedance: >1 MΩ
Input Bias Current (Burnout Detect): <1.5 µA
Overvoltage: ±10 V differential
Common Mode (Input to Ground): 600 Vac or 1000 Vdc max
LED Indications:
    Input Range (Green);
      >100% Input: 8 Hz flash
      <0% Input: 4 Hz flash
    Setpoint (Red): Tripped; Solid red (one LED for each setpoint)
Limit Differential (Deadband): 0.25% to 50% of span
Response Time:
    Dynamic Deadband: Relay status will change when propersetpoint/process condition exists uninterrupted
    for 100 msec
    Normal Mode (Analog Filtering): <250 msec (10 to 90%)
    Effectivity: Setpoints are adjustable over 100% of input span
    Repeatability (Constant Temp): ±0.2% for inputs > 0°C; ±0.3% for inputs < 0°C
    Line Voltage: ±0.01%/% max
    Temperature: ±0.05% of full scale/°C max
Common Mode Rejection (DC to 60 Hz): 120 dB
Isolation: 1000 Vdc between contacts, input and power
ESD Susceptibility: Meets IEC 801-2, Level 2 (4 KV)
    Operating: 15 to 95% RH @ 45°C (113°F)
    Soak: 90% RH for 24 hours @ 65°C (149°F)
Temperature Range:
    Operating: 0 to 60°C (32 to 140°F)
    Storage: -15 to 70°C (5 to 158°F)
Power: 120/240 Vac ± 10%, 50 to 60 Hz selectable, 2 W typical, 5 W max
Relay Contacts: 1 SPDT (1 Form C) per setpoint
    Current Rating (Resistive):
      120 Vac: 5A
      240 Vac: 2A
      28 Vdc: 5A
    Material: Silver-Cadmium Oxide
    Electrical Life: 105 operations at rated load (external relay contact protection is required for use with inductive loads)
    Mechanical Life: 107 operations
Latch Reset Time: 5 seconds (with power removed)
Weight: 291 g (0.64 lb)
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