The MKS 902B Absolute Piezo Vacuum Pressure Transducer is a device designed for accurate vacuum pressure measurement, offering RS232, RS485, and display options. This transducer provides a wide measuring range from 0.1 to 1000 Torr and is based on the measurement of thermal conductivity and mechanical deflection of a silicon membrane. It is suitable for general vacuum pressure measurement, vacuum pressure measurement in dirty and corrosive environments, fore line and roughing pressure measurement, gas backfilling measurement and controlling, system process control, and sensitive abnormal pressure and take appropriate security measure using set point relays and control system pressure.

Function Description:

The 902B transducer utilizes a single sensor element, a Piezo sensor, which is based on the mechanical deflection of a stainless steel 316 membrane relative to an integrated reference vacuum. This design ensures absolute pressure measurement independent of gas composition and concentration. The sensor element is robust and can withstand high G-forces and instant air inrush.

The transducer can be used in a variety of applications as a standalone unit or with the PDR900 display and controller unit. It features RS232 or RS485 digital communication interfaces for setup of transducer parameters and to provide real-time pressure measurement. For applications requiring interlocking valves or pumps, the analog voltage output can be interfaced to external analog equipment for pressure readout or control.

The 902B transducer offers several functions accessible via a user switch, including Vacuum Zero adjustment (ZER! Command) and Transducer firmware upgrade mode. An LED status indicator (red or green) provides visual feedback on the transducer's operational status and any detected faults.

Important Technical Specifications:

Measuring Range: 0.1 to 1000 Torr (absolute)
Accuracy: ±1% of reading (10-1000 Torr)
Repeatability: ±0.3% of full scale
Maximum Pressure: 1500 Torr
Supply Voltage: 9-30 VDC
Power Consumption: <1.2 Watt
Fuse (thermal recoverable): 200 mA
Analog Output (MKS standard): 0-10 VDC, 12 bit resolution, 100 Ω impedance, 16 Hz update rate.
Setpoint Relay Range: 1-1000 Torr
Setpoint Relay Contact Rating: 1A @ 30 VDC/VAC (resistive load)
Setpoint Relay Contact Resistance: 100 mΩ (max)
Setpoint Relay Contact Endurance: 100,000 (min) (1A @ 30 VDC load), 2,000,000 (min) (0.2 A @ 30 VDC load)
Setpoint Relay Response Time: <100 ms
Materials Exposed to Vacuum: Stainless Steel 316
Internal Volume:
- KF16 flange: 1.023 cm³
- VCR4 flange: 1.488 cm³
- VCR8 flange: 2.627 cm³
Electronics Casing Material: Stainless steel 304
Flange Material: Stainless steel 316
Weight:
- KF16 flange: 170 g
- VCR4 flange: 191 g
- VCR8 flange: 221 g
Operating Temperature: 0 to 40 °C (32 to 104 °F)
Bake out temperature (non-operating): 100 °C (212 °F)
Humidity: 0-95% Non-condensing
Ingress Protection Rating: IP40 (IP54 version available for harsh environments)

Usage Features:

The 902B transducer is designed for use in relatively clean environments. It is not recommended for use in corrosive environments like a semiconductor etch process chamber where aggressive gases like fluorine are used. The transducer can be mounted in any orientation without compromising performance or calibration.

The transducer offers an active and individual sensor temperature compensation circuit that ensures accurate measurement in a wide temperature range. It is suitable for measuring performance in a wide temperature gradient and direct cooling like air-condition air stream or direct heating like a pump exhaust stream. The transducer electronics can withstand 85 °C (185 °F) when the power is turned off.

For electrical connections, the 902B must be properly electrically connected according to specifications. Output pins are protected against wrong electrical connections. Wrong electrical connections can cause permanent damage to the transducer or interference to measuring performance.

The 902B transducer is available with different types of vacuum fittings. When mounting the transducer, ensure that all vacuum sealing items and surfaces are clean, without damage and free of particles. Do not touch the vacuum flange sealing surface. If the transducer will be exposed to pressures above atmospheric pressure, make sure that proper vacuum fittings are used. Ensure that the internal system pressure is an ambient pressure before opening the vacuum system and removing any connections.

The power supply input is 9 to 30 VDC. The power supply input is protected by an internal thermal fuse. The fuse is self-recoverable; do not replace it. Damage may occur to the circuitry if excessive voltage is applied, polarity reversed or if a wrong connection is made.

The 902B supports various communication protocols, including RS232 and RS485. The RS232 interface is typically used for Data Communication Equipment (DCE) and can be connected to a PC. The RS485 interface is a network communication system that enables the user to communicate with several units on the same communication line. It allows for longer cable spans (up to 1,200m (4,000 ft)) compared to RS232.

The transducer features an integrated touch display for easy access to setpoints, sensors, model, and measurements units. A pressure threshold alarm can be set and the transmitters with multiple sensors. The display allows users to choose which sensor pressure value is displayed on the screen. The menu structure provides access to various settings, including Home, Menu, Sensor, Setpoints, Settings, Unit, Setup, and Alarm.

Maintenance Features:

Before unpacking the 902B Absolute Piezo transducer, check all surfaces of the packing material for shipping damage. Inspect for visible damage. If found, notify the carrier immediately. Check to be sure the 902B package contains the correct items.

The 902B transducer is factory calibrated when delivered and in most applications further calibration is not required. If the sensor element has been contaminated or damaged by process gases, adjustment of zero and full scale can be executed to compensate for measurement errors.

The measuring accuracy is specified as transducer reading ± a percentage of the actual pressure. The best measuring accuracy is factory calibrated and cannot be user adjusted. The repeatability specification is the transducers ability to repeat the same measurement value after multiple pressure cycles.

The Piezo zero adjustment can only be executed when the MicroPirani pressure measurement is below 0.1 Torr. The Piezo zero adjustment sets the Piezo zero reading. The factory default command resets all or certain parameters of the 902B to factory default settings as listed above. If other digital communication setup than factory default values are used, then the communication will be lost after execution of factory default and the transceiver equipment should be set to transducer values.

For firmware upgrades, the 902B firmware can be upgraded by the user via RS232. The procedure involves installing the 900 Series firmware download software, turning power off, holding down the User switch while turning power on, releasing the User switch, and running the firmware download software. Note that the transducer with RS485 interface cannot be firmware upgraded by the user and requires contacting MKS customer service for upgrade.

In case of troubleshooting, common symptoms and possible causes/remedies are provided. For example, no digital communication could indicate incorrect electrical connections, incorrect transducer address, or termination characters missing. Incorrect pressure values might be due to other gas presence, contaminated sensors, or corroded sensors. If the status LED is illuminating red, it indicates a sensor element defect, requiring service and repair.

The 902B transducer is manufactured according to the RoHS directive. For the benefit of the environment, at the end of life of the 902B, it should not be disposed of in the normal unsorted waste stream. It should be deposited at an appropriate collection point or facility to enable recovery or recycling.

MKS 902B - Page 53

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