GE IC695ALG508 | 8-Channel RTD Input Module – RX3i Service Manual

Description

Hard-Numbers: Technical Specifications

Parameter	Specification
Number of Channels	8 isolated differential inputs
RTD Input Types	Platinum 385 (50, 100, 200, 500, 1000Ω), Platinum 391.6 (50, 100, 200, 500, 1000Ω), Nickel 618 (100, 200, 500, 1000Ω), Nickel 672 (120Ω), Nickel-Iron 518 (604Ω), Copper 426 (10, 50, 100Ω)
Resistance Input Ranges	0-260, 0-525, 0-1050, 0-2100, 0-3150, 0-4200 ohms
Maximum RTD Lead Resistance	25Ω each side (50Ω total)
Excitation Current	0.238-1.654 mA (depends on input type)
Temperature Ranges	Platinum 385: -200 to +850°C; Platinum 391.6: -200 to +630°C; Nickel 618/672: -100 to +260°C; Nickel-Iron 518: -100 to +200°C; Copper 426: -100 to +260°C
Temperature Accuracy (4-wire)	Pt100 @ 25°C: ±0.7°C (typical), ±1.2°C (maximum over temp span)
Temperature Accuracy (1000Ω)	Pt1000 @ 25°C: ±0.5°C (typical), ±0.9°C (maximum over temp span)
Resistance Accuracy	250Ω: ±0.25Ω; 500Ω: ±0.3Ω; 1000Ω: ±0.5Ω; 2000Ω: ±0.9Ω; 3000Ω: ±1.3Ω; 4000Ω: ±1.7Ω
Repeatability	0.05% of span at constant temperature over 30-second period (0.1% for 10-ohm copper, 28Hz filter)
Channel Update Rate	120ms for all 8 channels
Notch Filters	2.3 Hz, 4 Hz, 4.7 Hz, 24 Hz, 28 Hz (selectable per channel)
Normal Mode Noise Rejection	2.3 Hz filter @ 50/60Hz: 67dB; 4 Hz filter @ 50Hz: 67dB, @ 60Hz: 80dB; 4.7 Hz filter @ 50/60Hz: 80dB; 24 Hz filter @ 50/60Hz: 25dB; 28 Hz filter @ 50/60Hz: 100dB
Common Mode Rejection	> 70dB (2/3-wire), > 90dB (4-wire), > 100dB (resistance inputs)
Channel-to-Channel Crosstalk	-70dB minimum
Data Format	16-bit integer (in 32-bit field) or 32-bit IEEE floating point
Measurement Units	Degrees Celsius, Degrees Fahrenheit, or Ohms (selectable)
Diagnostics	Over Range, Under Range, High/Low Alarm, High-High/Low-Low Alarm, Open Circuit Detection, Positive/Negative Rate of Change Alarm, Watchdog, RAM Fail, Flash Fail
Fault Reporting	Configurable enable/disable for each alarm type
Channel Behavior on Fault	Default to 0 or Hold Last State (configurable)
Isolation (Field to Backplane)	250VAC continuous; 1500VAC for 1 minute; 2550VDC for 1 second
Channel-to-Channel Isolation	Supported
Power Consumption	3.3V: 400mA; 5.1V: 200mA
Power Dissipation	2.5W maximum
Terminal Blocks	Box-style (IC694TBB032), Extended Box-style (IC694TBB132), Spring-style (IC694TBS032), Extended Spring-style (IC694TBS132) – sold separately
LED Indicators	Module OK, Field Status
Hot-Swap	Supported (per RX3i System Manual)
CPU Compatibility	RX3i Universal Backplane; Firmware version 5.5 or later required; Machine Edition version 5.8 or later for configuration
Operating Temperature	0°C to 60°C
Storage Temperature	-40°C to 85°C
Humidity	5% to 95% non-condensing
Weight	0.56 lbs (0.26 kg)
Dimensions	145mm x 140mm x 34mm (5.71″ x 5.51″ x 1.34″)
Approvals	UL, UL HAZLOC, CE, ATEX C1D2, ABS, BV, DNV, GL, KRS, LR

GE IC695ALG508

The Real-World Problem It Solves

• Chemical processing plants monitoring reactor vessel temperatures and heat exchanger performance
• Food & beverage production tracking oven, freezer, and pasteurization temperatures
• Pharmaceutical manufacturing validating sterilization and fermentation temperature profiles
• Power generation monitoring steam turbine and generator cooling system temperatures

Hardware Architecture & Under-the-Hood Logic

1. RTD sensor (Pt100, Pt1000, Ni, Cu, etc.) connected via terminal block (2/3/4-wire)
2. Module applies precision excitation current (0.238-1.654 mA depending on sensor type)
3. Differential input measures voltage across RTD (compensating for lead resistance in 3/4-wire mode)
4. Programmable notch filter (2.3-28Hz) removes electrical noise and interference
5. ADC converts filtered analog signal to digital value
6. CPU applies ITS-90 linearization algorithm based on RTD type
7. Linearized temperature stored in dual-port memory (16-bit integer or 32-bit float)
8. PLC CPU reads temperature during scan cycle via backplane
9. Diagnostics circuitry monitors for open circuit (wire-off), over/under range, rate of change
10. Alarm status bits updated for enabled diagnostic conditions
11. LED drivers illuminate Module OK and Field Status indicators
12. Fault configuration (default 0 vs hold last state) applied when fault detected

• Platinum 385 (50Ω): 1.175 mA
• Platinum 385 (100, 200, 500, 1000Ω): 0.717 mA
• Platinum 391.6 (50Ω): 1.175 mA
• Platinum 391.6 (100, 200Ω): 0.717 mA
• Platinum 391.6 (500, 1000Ω): 0.238 mA
• Nickel 618 (100, 200Ω): 0.717 mA
• Nickel 618 (500, 1000Ω): 0.238 mA
• Nickel 672 (120Ω): 0.717 mA
• Nickel-Iron 518 (604Ω): 0.238 mA
• Copper 426 (10Ω): 1.654 mA
• Copper 426 (50, 100Ω): 1.175 mA

• Module switches to measure lead resistance every 100 samples
• Measured lead resistance used to compensate next 100 samples
• Automatic compensation eliminates lead wire error (up to 25Ω per side)
  

  GE IC695ALG508

Field Service Pitfalls: What Rookies Get Wrong

• Field Rule: Always use 3-wire or 4-wire for Pt100 sensors with cable runs > 2 meters. 4-wire provides best accuracy (compensates both lead resistances). 2-wire only for short runs (<1 meter) where lead resistance is negligible.

• Field Rule: Verify RTD standard stamped on sensor housing (α = 0.00385 vs α = 0.003916). Match software configuration to sensor type exactly. Check sensor datasheet for IEC 751 vs JIS 1604 standard compliance.

• Field Rule: Select notch filter based on environment: 2.3 Hz for DC environments, 4-4.7 Hz for 50Hz power, 24 Hz for 60Hz power, 28 Hz for both frequencies. Use higher filter (24-28Hz) if readings drift with nearby VFDs or motors.

• Field Rule: Calculate total lead resistance: wire resistance per meter × cable length (both directions). For 3-wire, add both lead resistances. Maximum 25Ω per side (50Ω total). Use 4-wire or larger resistance RTDs (Pt1000) for long cable runs.

• Field Rule: Configure rate-of-change alarm based on process thermal mass and response time. For large thermal mass (reactors, vessels), use 1-5°C/min. For fast response (heat exchangers), use 5-10°C/min. Test alarms during commissioning.

• Field Rule: Use “Hold Last State” only for non-critical monitoring or redundant systems. Configure safety-critical temperature channels to “Default to 0” (or safe fail-safe value) on fault detection to trigger safe shutdown.

• Field Rule: Use Extended Box-style (IC694TBB132) or Extended Spring-style (IC694TBS032) for shielded cable installations. Extended blocks provide extra shroud depth for proper shield termination. Standard blocks (IC694TBB032/TBS032) only for unshielded wiring.

• Field Rule: Always enable “Periodic Lead Resistance Compensation” for 3-wire RTDs in configuration software. Module automatically measures lead resistance every 100 samples and compensates for next 100 cycles. This eliminates lead resistance drift due to temperature changes.

• Field Rule: Verify sensor type before configuration. RTD sensors are metallic (Pt, Ni, Cu) with predictable resistance-temperature curves. Thermistors are semiconductor devices with exponential curves. Use “Resistance Input” mode for generic resistance measurement (0-4200Ω ranges).

• Field Rule: Calculate acceptable lead resistance based on accuracy requirement. For Pt100 (0.1°C accuracy), total lead resistance must be < 0.4Ω. Use 18AWG or 16AWG for runs > 10 meters. Wire gauge must be consistent for all 3-wire connections to ensure proper compensation.

• Field Rule: Monitor both Module OK (green = good) and Field Status LEDs. Field Status LED indicates external 24VDC supply status and fault presence. If Field Status LED is off or red, check external 24VDC supply voltage and connections before troubleshooting individual channels.

• Field Rule: Verify RX3i CPU firmware version is 5.5 or later before installing IC695ALG508. Upgrade CPU firmware if necessary. Use Proficy Machine Edition version 5.8 or later for module configuration. Incompatible with Series 90-30 PLC CPUs.