1 Description
目的
This application note explains how the Set Point 1 open-collector output of a Televac® MX2A or MX4A rough vacuum active gauge can be used to automatically control the turn on and turn off of a Televac® MP7ER or MP7FR cold cathode high vacuum active gauge.
Applicable Products
This application note applies to the following Televac® products and cables:
| 説明 | 部品番号 |
|---|---|
| エムエックスツーエー | 2-8910-1XX |
| エムエックスフォーエー | 2-8930-1XX |
| ＭＰ７ＥＲ | 2-7950-XXX |
| エムピーセブンエフアール | 2-7970-XXX |
| MX2A/MX4A 6芯ケーブル | 2-9857-XXX |
| MP7ER/MP7FR 9芯ケーブル | 2-9852-XXX |
2 How the Automatic Control Works
The Televac® MX2A and MX4A are thermal conductivity active vacuum gauges used for rough vacuum measurements from approximately 1*10-3 to 1000 Torr.
The Televac® MP7ER and MP7FR are cold cathode active vacuum gauges used for high vacuum measurements from approximately 1*10-11/1*10-8 Torr to 1*10-2 Torr.
Cold cathode gauges should not be operated at pressures above approximately 1*10-2 Torr. Operating the cold cathode at higher pressures can increase sputtering, oxidation, and contamination, which may lead to inaccurate readings and damage to the vacuum gauge.
Because the MP7ER and MP7FR cannot measure above approximately 1*10-2 Torr, the MX2A or MX4A can be used to determine when the cold cathode vacuum gauge should be turned on or off.
The MX2A and MX4A include an open-collector Set Point 1 output that can be configured to switch at a specific vacuum pressure. For this application, the set point is configured near 1*10-2 Torr and connected directly to the cold cathode turn on/off control input of the MP7ER or MP7FR.
This creates a standalone active vacuum gauge system in which the MX2A/MX4A measures rough vacuum and controls the cold cathode, while the MP7ER/MP7FR measures high vacuum. The combined system can cover the pressure range from approximately 1*10-11/1*10-8 Torr to 1000 Torr.
3 Configure MX2A/MX4A Set Point 1
The MX2A/MX4A Set Point 1 open-collector output uses two pressure settings:
- SP1L (Set Point 1 Low): Pressure at which the set point activates.
- SP1H (Set Point 1 High): Pressure at which the set point deactivates.
For automatic control of an MP7ER or MP7FR, the following settings are recommended:
| Setting | Recommended Value | Equivalent Pressure |
|---|---|---|
| SP1L | 0.010 Torr | 10 mTorr / 10 microns / 1.0*10-2 Torr |
| SP1H | 0.012 Torr | 12 mTorr / 12 microns / 1.2*10-2 Torr |
These values provide separate turn-on and turn-off pressures for the cold cathode gauge. These settings are recommendations; your vacuum system may require different values.
To configure SP1L and SP1H from the MX2A/MX4A front panel:
- From the measurement screen, press the SEL key twice.
- The display will show Setpoint SP1L .XXX, where .XXX is the current setting.
- Press ENT. ADJ will appear at the top center of the display.
- Use the up and down arrows to adjust the value to .010.
- Press ENT to save the setting. ADJ will disappear.
- Press the down arrow. The display will show Setpoint SP1H .XXX.
- Press ENT. ADJ will appear again.
- Use the up and down arrows to adjust the value to .012.
- Press ENT to save the setting. ADJ will disappear.
- Press SEL three times to return to the measurement screen or allow the display to return automatically after the timeout.
The SP1L and SP1H settings can also be configured through RS-485 communications using the W2 command.
To configure the recommended values above, send:
*XW210021202<cr>
Where:
- X is the MX2A/MX4A address. The default is 0.
- <cr> represents a carriage return which is equivalent to pressing the enter key on your keyboard.
4 Connect the MX2A/MX4A and MP7ER/MP7FR
These instructions assume the use of the following Televac® cables:
- MX2A/MX4A 6 Conductor Cable: PN 2-9857-XXX
- MP7ER/MP7FR 9 Conductor Cable: PN 2-9852-XXX
After configuring Set Point 1 as described in Section 3, make the following connections.
| MX2A/MX4A | MP7ER/MP7FR | 説明 |
|---|---|---|
| ピン 5 (緑) | ピン1（茶色 | Set Point 1 connection to the cold cathode turn on/off control pin |
| ピン12（黒 | 説明を参照してください。 | Connect to power supply (-) ground |
| ピン 8 (赤) | ピン 4 (黄) | Power supply (+), 24 V DC; these connections may be made independently |
| ピン15（黒 | ピン 2 (赤) | Power supply (-) ground; these connections may be made independently |
The wiring grounds the source connection of MX2A/MX4A Set Point 1 and connects the open-drain output to the MP7ER/MP7FR cold cathode control input.
During pumpdown, when the pressure reaches 1.0*10-2 Torr, Set Point 1 activates and connects the MP7ER/MP7FR cold cathode control input to ground, turning the cold cathode on.
During venting or pressure rise, when the pressure reaches 1.2*10-2 Torr, Set Point 1 deactivates and disconnects the control input from ground, turning the cold cathode off.
The wires shown in the connection table do not need to be connected directly to each other. They may be routed through a terminal block or other appropriate connection point in the system.
Additional system connections may also be required. For example:
- The 0 to 10 V DC analog outputs may be connected to analog inputs on the PLC.
- The RS-485 connections may be connected to a PLC or other control system.
5 Alternative Control Methods
The configuration described in this application note is one method for automatically controlling the MP7ER/MP7FR cold cathode using an MX2A/MX4A. Depending on the requirements of the vacuum system, other control methods may be more appropriate.
Alternative methods include:
- Use the MX2A/MX4A Set Point 2 relay to control the MP7ER/MP7FR cold cathode turn on/off input.
- Monitor the MX2A/MX4A analog output with a PLC or other control system, convert the analog output to a vacuum pressure reading, and use the control system to switch the MP7ER/MP7FR cold cathode at approximately 1*10-2 Torr (10 mTorr / 10 microns).
- Monitor the MX2A/MX4A vacuum pressure using RS-485 communications and use the PLC or other control system to control the MP7ER/MP7FR cold cathode based on the measured pressure.