F2-04RTD New Original F204RTD Facts Engineering Temperature Module

Product Description

Facts Engineering F2-04RTD — DL205 4-Channel RTD Temperature Input Module | 16-Bit | Pt100 / Pt1000 / jPt100 / Cu10 / Cu25 | Auto-Calibration | New Original

Temperature measurement in industrial PLC systems splits cleanly into two categories. There's the quick-and-rough approach — an analog input card reading a 4–20mA transmitter that someone has already scaled, with all the error stacking that entails: sensor tolerance, transmitter span error, analog input offset, scaling rounding. Then there's the direct approach: an RTD input module that connects the sensor wire directly to the module, runs the NIST linearization internally, and puts a calibrated temperature value straight into V-memory. No transmitter, no conversion math in the ladder, no accumulated scaling error.

The F2-04RTD takes the direct approach. Four differential RTD input channels, charge-balancing 24-bit conversion, automatic five-second recalibration, and built-in support for five RTD types — including European Pt100, American jPt100, Pt1000, and both copper variants — all inside a single DL205 slot. The result is a temperature reading accurate to ±1°C maximum inaccuracy with 0.1-degree resolution, ready to use in ladder logic or an HMI tag without any additional scaling block.

✅ Genuine Facts Engineering / AutomationDirect. New original in stock. Ships worldwide via DHL / FedEx / UPS.

Technical Specifications

The Five RTD Types — Which One to Select

All four channels of the F2-04RTD share a single RTD type, selected by hardware jumpers on the module's PC board. Choosing correctly at installation time is important because swapping types later requires physically accessing the jumper bank.

Pt100Ω (European curve) — The default factory setting and by far the most common RTD type in modern industrial applications. Calibrated to DIN 43760 / IEC 751 specification: 100Ω at 0°C, alpha = 0.00385 Ω/Ω/°C (100°C = 138.5Ω). This is the correct selection for the overwhelming majority of commercially available industrial RTDs from any manufacturer unless the documentation explicitly states otherwise. Range: –200.0°C to +850.0°C.

jPt100Ω (American curve / JIS curve) — Platinum 100Ω RTDs manufactured to the older American or Japanese curve: alpha = 0.00392 Ω/Ω/°C. Physically identical to European Pt100 sensors but with a slightly different resistance-temperature relationship. The European curve (IEC 751) has largely replaced this standard in new equipment, but existing installations — particularly in older US or Japanese facilities — may use jPt100 sensors. Range: –38.0°C to +450.0°C.

Pt1000Ω — Platinum RTD with 1000Ω resistance at 0°C rather than 100Ω. The higher resistance makes Pt1000 sensors less sensitive to lead wire resistance effects, which is useful in installations with long cable runs where a 1Ω lead resistance represents a much smaller percentage of the total circuit resistance than it would with a Pt100. Range: –200.0°C to +595.0°C.

Cu10Ω and Cu25Ω — Copper RTDs with 10Ω or 25Ω nominal resistance at 0°C. Copper RTDs are less stable than platinum types over time and have a narrower useful temperature range, but they remain in service in older process equipment, transformer winding temperature monitoring, and some motor protection applications. Both types cover the same range of –200.0°C to +260.0°C.

How the Auto-Calibration Works

One of the less-obvious but genuinely important features of the F2-04RTD is its automatic five-second recalibration cycle. Every five seconds, the module's internal circuitry performs offset and gain self-correction, removing any drift that has accumulated since the last calibration. This happens continuously and automatically with no PLC program intervention and no interruption of measurement output.

The practical implication is long-term measurement stability without periodic manual recalibration. In a continuous process environment — a kiln running 24 hours a day, an extruder running across multiple production shifts, a water treatment system operating year-round — the temperature readings remain accurate as the module's components age, as panel temperature fluctuates through daily cycles, and as power supply voltage drifts slightly. The chopper-stabilized programmable gain amplifier and ratiometric referencing architecture underpin this behavior, but the five-second calibration cycle is what the end user sees in practice: a module that doesn't need attention.

For processes with extremely tight temperature tolerance requirements, the module also supports user offset correction via ladder logic — a constant can be added or subtracted to any channel's reading to correct for known RTD tolerance offset, without affecting the other channels.

Lead Wire Compensation and Wiring Fundamentals

An RTD works by measuring the electrical resistance of a sensing element — typically platinum wire — whose resistance changes predictably with temperature. The complication is that the copper wires running from the module to the sensor also have resistance, and if that lead resistance is lumped in with the sensor reading, the temperature measurement will be wrong. The longer the cable run and the smaller the wire gauge, the worse this error becomes.

The F2-04RTD handles this with dual matched current sources and ratiometric measurement — a hardware architecture that directly compensates for lead wire resistance rather than relying on a software correction factor. The standard connection uses a three-wire configuration: one wire to CH+, one to CH–, and one to COM. The compensation circuitry uses the COM path to measure and null out the lead resistance, leaving a reading that reflects only the sensor element itself.

For four-wire RTD sensors (which include a dedicated sense pair to eliminate lead resistance by a different method), the module wiring is adapted by leaving the second CH+ sense wire unconnected. The module still operates correctly with a four-wire sensor; the extra wire simply isn't used.

Two wiring points that the official manual emphasizes explicitly: the three wires connecting any one RTD to the module must be the same type and same length — mismatched wires produce asymmetric resistance that the compensation circuit cannot fully correct. And unused channels should have their CH+ and CH– terminals shorted to the COM terminal; leaving them open can introduce noise into adjacent channels through the multiplexed measurement circuit.

The module's RTD excitation current is only 200µA, resulting in a worst-case self-heating dissipation of 0.016mW in a connected Pt100 RTD. At that power level, Joule heating in the RTD element is negligible — it won't introduce a measurable temperature offset from self-heating even in low-airflow sensor installations.

Channel Scanning and V-Memory Data Structure

The F2-04RTD presents itself to the DL205 CPU as a 32-point discrete input module rather than an analog module. Temperature data arrives in the CPU's V-memory, with the actual slot placement determining the base X address from which the 32 input points are mapped.

Each channel's 16-bit data word contains: 15 binary data bits carrying the temperature value (with one implied decimal place — a V-memory value of 1002 means 100.2°C or °F), one sign bit, two channel ID bits that identify which channel the reading came from, and four fault bits covering conditions such as short circuits and input power loss. The fault bits are accessible as discrete input points in the ladder, making it straightforward to build alarm rungs that trigger on sensor failure.

The update rate depends on which CPU is installed. With a D2-240, D2-250-1, D2-260, or D2-262 CPU, all four channels are captured within a single scan using the pointer method and dedicated V-memory locations designed for this purpose. With a D2-230 CPU, the module uses the multiplexing method: one channel per scan, cycling through channels 1–4 across successive scans. In a typical application with a D2-230 running a few hundred millisecond scan cycle, the maximum latency for a new temperature reading from all four channels is under two seconds — entirely adequate for thermal processes with time constants measured in seconds or minutes.

Negative temperatures are stored as either 2's complement or magnitude plus sign, selected by jumper. Both formats are supported in DirectSOFT's data display elements; the Signed Decimal format correctly interprets 2's complement data.

DL205 CPU Compatibility Requirements

The F2-04RTD can be installed in any slot of a DL205 baseplate, including remote I/O bases, provided the CPU firmware meets the minimum version requirements:

D2-230: firmware version 1.6 or later is required. Additionally, the D2-230 has a special placement constraint: the module's first input address must fall on a V-memory boundary address for the data to be accessible via the required V-memory references. The DL205 Analog I/O Manual provides the valid starting X addresses and their corresponding V-memory locations.

D2-240: firmware version 2.5 or later is required. No placement constraints — standard slot assignment rules apply.

D2-250: firmware version 1.06 or later is required.

D2-260 and D2-262: no special firmware notes are documented in the manual.

Checking the CPU firmware version before ordering or installing the F2-04RTD into an existing DL205 system avoids the situation where the module is physically installed but the CPU firmware is too old to read data from it correctly.

Selecting the Right Analog Temperature Module for DL205

The DL205 platform supports several temperature input options, each suited to different sensor types:

If the temperature sensors already installed are platinum RTDs — the most common choice for general industrial process temperature measurement in the 0–500°C range — the F2-04RTD is the correct module. If sensors are thermocouples, the F2-04THM handles type-matched thermocouple signals with internal cold junction compensation. If the temperature sensing is done in a field transmitter outputting 4–20mA, any of the analog input modules will work without the RTD module.

❓ FAQ — Facts Engineering F2-04RTD

Q1: Can each of the four channels use a different RTD type simultaneously — for example, two Pt100 and two Cu25?

No. The RTD type is selected by hardware jumpers on the module's PC board and applies to all four channels simultaneously. All four channels must use the same RTD type. This is a fundamental characteristic of the module's design: a single set of linearization coefficients and excitation current level is applied across all channels. If an application genuinely requires different RTD types in the same system, the solution is to use multiple F2-04RTD modules — one per RTD type — each configured with its own jumper setting. Because the module occupies a standard DL205 slot and draws only 90mA from the backplane 5V bus, running two modules simultaneously is straightforward in terms of both space and power budget in a DL205 rack.

Q2: What is the difference between 2-wire, 3-wire, and 4-wire RTD connections, and which should be used with the F2-04RTD?

The F2-04RTD is designed for the 3-wire configuration and uses it as the standard connection. In a 3-wire setup, one lead goes to CH+, one to CH–, and the third to COM. The module's dual matched current sources and ratiometric measurement circuitry use the COM path to measure and cancel the lead wire resistance, delivering a reading that reflects only the sensor element. For 4-wire sensors — which use separate source and sense pairs to provide their own lead compensation — only three of the four wires are connected to the module: CH+, CH–, and COM, with the additional sense wire left unconnected. Two-wire connections are not recommended because there is no compensation path, and any lead resistance adds directly to the measured resistance, producing a temperature reading that reads high by an amount proportional to the lead wire resistance.

Q3: Does the F2-04RTD require any special programming or ladder logic configuration?

Beyond placing the module in the rack and ensuring the CPU firmware meets the minimum version, the F2-04RTD requires minimal programming. The temperature data appears directly in V-memory locations mapped to the module's 32 discrete input points without any ladder instructions needed to trigger conversion or manage mode registers. Reading a temperature value is as simple as a LD (load) instruction referencing the appropriate V-memory word. The module does not require an initialization routine or a mode-selection write from the CPU. For CPUs in the D2-240 and later family, the pointer method allows all four channels to be captured in a single scan, and the manual provides the specific V-memory ladder example. The only software tool requirement is DirectSOFT version 4.0 or later for programming the DL205 CPU.

Q4: How does the 5-second auto-calibration cycle affect real-time measurement?

The auto-calibration runs in the module's own internal circuitry asynchronously with the CPU scan. From the PLC program's perspective, temperature data in V-memory is updated continuously — the calibration cycle does not cause the V-memory value to freeze, jump, or go invalid during the calibration interval. The calibration corrects offset and gain drift accumulated since the last cycle, so the effect on any individual reading is a very small correction that keeps measurements tracking within specification over time. In practice, a properly installed F2-04RTD with good RTD sensors and correctly routed shielded cable will show temperature stability well within the ±1°C maximum inaccuracy specification without the user needing to think about the calibration cycle at all.

Q5: What do the fault bits indicate, and how are they accessed in the ladder program?

Each channel's 16-bit data word includes 4 fault bits that report the status of the channel's measurement. These bits detect conditions including short circuits across the RTD input terminals and input power disconnection (open circuit at the RTD). Because the F2-04RTD presents itself as a 32-point discrete input module, each of the 32 assigned X input addresses corresponds to a specific bit in the module's data output. The fault bits for each channel are accessible as discrete input contacts in the ladder program — a normally open contact referencing the fault bit for Channel 1 will close if Channel 1 reports a fault, triggering whatever alarm, output, or notification logic the programmer wires to it. This makes building sensor-loss alarms straightforward: one rung per channel with an output coil driving an alarm indicator or an HMI tag.

Q6: The F2-04RTD needs 32 input points from the CPU — does this significantly impact the DL205 I/O budget?

The 32 discrete input points consumed by the F2-04RTD come out of the DL205 system's total I/O point budget. In a typical DL205 rack, this is the same footprint as two 16-point discrete input modules. For systems with plenty of available I/O points, this is inconsequential. For systems near their I/O point limit, it's worth counting before installation. With a D2-230 CPU, placement also matters: the module's first input address must fall on a V-memory boundary, which constrains where in the slot order the F2-04RTD can be placed relative to other discrete modules. The D2-240, D2-250, D2-260, and D2-262 CPUs don't have this placement constraint and allow the module in any available slot.

Q7: Is the F2-04RTD suitable for measuring temperatures below 0°C, and how are negative temperatures displayed?

Yes. All five supported RTD types extend well below 0°C — Pt100 goes down to –200°C, jPt100 to –38°C, and the copper types to –200°C as well. Negative temperatures are stored in the module's data word with the most significant bit set as a sign bit, and can be represented in either magnitude plus sign or 2's complement format, selected by module jumpers. Magnitude plus sign stores the temperature value as a positive number with the sign bit indicating polarity — simple to interpret directly. 2's complement stores the signed value in standard binary two's complement form, which is required for correct display on some operator interfaces and can simplify mathematical operations like averaging across channels when both positive and negative values may appear. DirectSOFT's Signed Decimal display mode correctly interprets 2's complement data for display on the programming terminal; HMI tags should be configured to match whichever format the module is set to output.