What is the KOBOLD PAD differential pressure transmitter?
The KOBOLD PAD is a microprocessor-based differential pressure transmitter designed for flow, level, and pressure measurement. It measures differential, gauge, or absolute pressure and transmits a 2-wire 4-20 mA signal with digital HART protocol. Calibrated spans run from 0.3 inch W.C. to 6000 PSIG, with reference accuracy of ±0.075% of calibrated span on ranges 3 through 0.
Flow, level, and pressure applications
The PAD is designed to cover flow, level, and pressure measurement from one platform. For flow, it can be paired with primary elements such as orifice plates, using a stationary sensing principle with no moving parts in the flow path. For level, it measures hydrostatic pressure in open or pressurized vessels.
- Flow: designed to pair with primary flow elements such as orifice plates; the PAD-F model adds a totalizing function and measures flow rate from differential pressure without temperature or static pressure compensation.
- Level: measures hydrostatic pressure at the vessel bottom against atmospheric pressure in open tanks or vapor-space pressure in closed vessels, an approach that can help where direct contact with the process media is best avoided.
- Pressure: measures differential, gauge, or absolute pressure based on the selected model and sensor input.
For larger line sizes, the PAD can be paired with KOBOLD KPL differential pressure orifice plates, allowing the transmitter and primary element to be selected and serviced independently.
Operating principle and sensor technology
The PAD is a smart, loop-powered transmitter built around a capacitance sensor on the PAD-D, -F, -G, and -H models, or a piezoresistive sensor on the PAD-A. The sensor converts the pressure signal to a digital value, and the electronics apply stored correction coefficients before scaling the 4-20 mA output.
Sensor information and correction coefficients are held in EEPROM separately from the MCU module, which supports repair, reconfiguration, and replacement.
Ranges, accuracy, and turndown
Calibrated spans cover 0.3 inch W.C. through 6000 PSIG across range codes 2 to 0, and zero and span values can be set anywhere within the range limits. Reference accuracy is ±0.075% of calibrated span on ranges 3 through 0 and ±0.25% on range 2. Long-term stability is 0.125% URL over 36 months.
Turndown is 100:1 on ranges 4 through 0, 50:1 on range 3, and 20:1 on range 2.
Output, communication, and configuration
The PAD provides a two-wire 4-20 mA output, configurable for linear or square-root response, with a digital HART signal superimposed on the loop. Through HART, the transmitter can be configured remotely using a hand-held terminal or PC configurator, so settings can be adjusted without interrupting the process.
Configurable items include engineering units, 4-20 mA range points, damping from 0.25 to 60 seconds, and tag, descriptor, and message fields. A 5-digit LCD shows the reading at the device.
Construction and hazardous-area approvals
Wetted parts use 316L stainless steel isolating diaphragms, with 316 stainless steel drain and vent valves, flanges, and adapters, plus silicone oil fill fluid. The housing is aluminum or stainless steel, rated flameproof (Ex d) and waterproof to IP67. FKM O-rings are standard, and PTFE is available as an option.
ATEX approvals include II 2G Ex db IIC T6 to T4 Gb, II 2D Ex tb IIIC T85°C to T130°C Db, and an optional intrinsically safe II 1G or 2G Ex ia IIC T5 or T4 rating.
Process connections and mounting
Standard process connections are 1/4 inch NPT, with a 1/2 inch NPT process adapter offered as an option. A multi-planar process connection option supports vertical installation regardless of the process line orientation, without separate adapters or brackets. Diaphragm seals can be supplied for a range of connections.
A 304 stainless steel bracket is available for 2-inch pipe mounting, and 2-way, 3-way, and 5-way manifold valves can be supplied for direct mounting.
Application Guide Required for Product Specification
This product requires completion of our Application Guide before specification and ordering.
This product line offers multiple configuration options and technical specifications that must be precisely matched to/calibrated for your specific application requirements. Unlike standard configurable items, these products are engineered solutions that require detailed application information to ensure optimal performance.
The Process
- Complete the Application Guide - Provide detailed information about your specific application
- Technical Review - Our engineering team reviews your requirements
- Product Specification - We specify the exact configuration for your needs
- Quotation & Ordering - Receive your custom quote with precise part numbers
Important Notice
Unless this is a repeat order of a previously specified product with Kobold, we cannot accept orders or provide quotations without a completed Application Guide. Product numbers selected without proper application review may not meet your system requirements and could result in performance issues or compatibility problems.
Even if you believe you’ve identified the correct part number, the Application Guide process is required to verify compatibility and ensure a streamlined quote/order process.
Ready to get started?
The PDF Application Guide can be downloaded directly from this product page in the “Resource Tab” below and is also attached to the end of the product datasheet. Completed forms can be submitted to customerservice@koboldusa.com.
Need help filling it out? Contact our engineering team: call 412-788-2830 or schedule a free online engineering consultation at your convenience.
Common Questions about PAD - Heavy-Duty Industrial Differential Pressure Transmitter
The PAD family includes the PAD-D differential transmitter (static pressure to 2000 PSI), the PAD-F differential transmitter with pulse output and totalizer for flow, the PAD-H for high line pressure (static pressure to 4495 PSI), the PAD-G gauge transmitter, and the PAD-A absolute transmitter. Sensor input is user-selectable.
Process media temperature is rated from -4 to 248°F (-20 to 120°C). Ambient temperature is rated from -4 to 176°F (-20 to 80°C), and storage from -4 to 185°F (-20 to 85°C), non-condensing. The humidity limit is 5 to 100% RH. Maximum ambient at the LCD is 176°F (80°C).
The PAD operates on 12 to 45 VDC, with 17.5 to 45 VDC required for HART communication. Loop load is 0 to 1500 ohms in operation and 250 to 550 ohms for HART. Maximum load is 250 ohms at 17.5 VDC and 550 ohms at 24 VDC.
Yes. The PAD provides automatic ambient temperature compensation, and the transmitter software compensates for thermal effects using correction coefficients characterized across the sensor range. This design is intended to help hold measurement stability when ambient and process conditions change, without manual adjustment.
Yes. The PAD-F variant provides a frequency (pulse) output with a totalizer, so it can report instantaneous flow rate and cumulative volume. Pulse width is selectable at 10, 50, or 100 ms, the output is open collector rated 30 V and 500 mA, and the pulse rate reaches 49 pulses per second.
The fail-mode process function drives the output to a fail-high current of 21.1 mA or higher, or a fail-low current of 3.78 mA or lower. Response time is 120 to 200 ms within 10 to 90% of full scale, and turn-on time is 3 seconds.
The electrical connection is a 1/2 inch NPT conduit entry with M4 screw terminals, with a G1/2 option. Standard ingress protection is IP67 (protection code S). Optional ATEX ratings cover flameproof (Ex d) and intrinsically safe (Ex ia) versions for hazardous areas.
Order codes follow model, version, calibrated span, fill, process connection, electrical connection, approval, and option, as in PAD-D EE 2 S 2 N S0 0. Option C (engineering unit) is required when the transmitter is used as a flowmeter, and option V (square-root transfer function) applies only to the PAD-D and PAD-H.