DS4815PRTA | GE Factory Tested & ISO Certified

Description

Product Introduction

RTDs are the gold standard for precision temperature measurement—and the DS4815PRTA is the board that reads them. This Mark V module handles 8 independent RTD inputs, typically connected to platinum 100Ω sensors (Pt100) in 3-wire configurations. It’s used for bearing temperature monitoring (where a single degree matters), stator winding temperature in generators, and inlet air temperature measurement for efficiency calculations.

Compared to the DS4815PRT (non-A revision), the “A” revision adds a significant accuracy improvement—the previous 18-bit ADC was replaced with a 24-bit delta-sigma converter, increasing resolution from 0.03°C to 0.002°C. The excitation current was also reduced from 1mA to 500µA to minimize self-heating of the RTD (which can introduce errors in small sensors). The terminal assignment is identical—direct drop-in. However, if you’re using 4-wire RTDs, the A revision supports a true Kelvin connection (which the old unit did not); but the pinout for 4-wire is different, so consult the manual.

Key Technical Specifications

Compatible Replacement Models

Frequently Asked Questions (FAQ)

Q: What’s the difference between 3-wire and 4-wire RTD configurations on the PRTA?
3-wire is the most common configuration, using one excitation lead and two sense leads. The board compensates for lead resistance up to 25Ω, but the compensation assumes all three leads have the same resistance. 4-wire uses two excitation leads and two sense leads—it completely eliminates lead resistance errors by measuring the voltage across the RTD without current flowing through the sense leads. The PRTA supports both; you’ll need to change the configuration in the I/O map and wire accordingly. For high-accuracy applications (e.g., bearing temperature), 4-wire is recommended.

Q: How do I wire a 3-wire Pt100 to the PRTA?
Connect the sensor’s two sense wires (usually the same color) to the Input+ and Input- terminals, and the excitation wire (usually a third wire) to the Ex+ terminal. The board provides the excitation current. For example, for channel 1: terminal 1 (Ex+) goes to the excitation wire, terminal 2 (Input+) goes to one sense wire, terminal 3 (Input-) goes to the other sense wire. If you mix up the sense wires, the reading will be correct (they’re symmetrical)—but if you swap the excitation and sense, you’ll get a reading of 0 or open-circuit. Check GE’s manual GEK-108677 for diagrams.

Q: The temperature reading is 10°C higher than expected. What’s the likely cause?
Lead resistance mismatch. The 3-wire compensation assumes all three leads have the same resistance. If one lead has a bad connection or a different gauge, the compensation will be off—a 1Ω mismatch introduces about 2.5°C error for Pt100. Check the connections and ensure all three wires are the same length and gauge. If you have long cable runs, use 4-wire configuration to eliminate the issue. Also, check if you’ve selected the correct RTD type in the configuration (Pt100 vs. Pt1000)—mixing them up will give you wildly wrong readings.

Q: What’s the maximum cable length for RTD inputs?
With 3-wire configuration, cable length is limited by the lead resistance compensation range (max 25Ω). At 0.02Ω/foot for 18 AWG copper wire, that’s about 1250 feet (380m) per lead. In practice, we recommend keeping it under 500 feet to minimize noise pickup. With 4-wire configuration, there’s no theoretical limit—you’re only limited by noise, since the excitation current is constant and the sense leads carry negligible current. We’ve seen 2000-foot (600m) runs work with proper shielded cables.

Q: The self-heating error is a concern for small RTDs. How does the PRTA handle this?
The PRTA uses a 500µA excitation current, which dissipates only 25µW in a 100Ω Pt100 (I²R = 0.0005² × 100 = 25µW). That’s negligible—the temperature rise is less than 0.01°C. The earlier PRT used 1mA (100µW), which could cause 0.05°C self-heating in small sensors. If you’re using a tiny surface-mount RTD in a confined space, the PRTA’s lower excitation current is a significant advantage.

Q: The open-circuit detection is triggering on channel 5, but the RTD is connected. What’s the most common cause?
The PRTA checks for open circuit by looking for resistance >1000Ω. A 3-wire RTD that’s not wired correctly (e.g., the sense and excitation leads crossed) can cause the reading to go above 1000Ω. Also, a high-resistance connection (corroded terminal) can cause the same. Use an ohmmeter to measure the resistance between the Ex+ and Input+ terminals—it should be the RTD resistance (around 100-150Ω at room temperature). If it’s open, check the wiring at the RTD head.

Q: The PRTA shows a short-circuit on channel 2. What should I check?
Short-circuit detection trips when the resistance is below 0.1Ω. This usually means the excitation and sense leads are shorted together at the sensor head or at the terminal block. Check for a solder bridge on the RTD connection. If the short is not at the sensor, check the cable insulation—a nicked wire can short the leads. If you’ve ruled out wiring, the board’s internal front-end may be faulty—contact us for repair.

Q: Can I use the PRTA for 2-wire RTDs?
Technically yes—connect the 2-wire RTD across the Ex+ and Input+ terminals, and jumper Input- to the 0V return. But you’ll lose lead resistance compensation, and the reading will include the cable resistance (error). For accurate measurements, use 3-wire or 4-wire RTDs. If you only have 2-wire sensors, we recommend short leads and a calibration offset in the software.

Q: The conversion time is 100ms per channel. Does that mean the total scan time for 8 channels is 800ms?
Yes—the ADC sequentially samples each channel. The 100ms setting gives you a full update of all 8 channels every 800ms. If that’s too slow for your control loop, you can reduce the conversion time to 50ms (total 400ms) or 25ms (total 200ms) in the I/O map. However, reducing the conversion time increases the noise—at 25ms, the effective resolution drops to about 18-bit. For bearing temperature (slow-changing signals), 100ms is fine. For fast transients (e.g., flame detection), you’d need a thermocouple or high-speed module.

Q: Does the PRTA support Pt1000 RTDs?
Yes—the board supports Pt1000 sensors. You’ll need to select Pt1000 in the I/O map for each channel. The excitation current is the same (500µA), which works well with Pt1000. The lead resistance error is proportionally smaller for Pt1000 (because the sensor’s resistance is 10x higher), so 3-wire compensation is more accurate.

Q: What’s the lead time for a surplus PRTA?
We keep 4-6 units in stock. Domestic: 2-3 business days ground, overnight if ordered by 2 PM EST. International: 5-7 days via DHL, with customs potentially adding 1-3 days. This board is not ITAR-controlled, so we can ship to most countries without an export license. We include a GE certificate of origin and commercial invoice with every shipment. If you need expedited shipping for a critical outage, contact us directly—we can arrange DHL Express Same-Day for urgent cases.

A-B 1756-RM/A
VIBRO MPC4
PROSOFT PLX82-EIP-PNC
KOLLMORGEN PRD-P310250Z-55