This application note explains how the relay set point of an MX2A or MX4A rough vacuum active gauge can be used to automatically enable and disable an MX7B or MX7M cold cathode high vacuum active gauge.
Relevant Televac® Products
This application note applies to the Televac® products listed below:
|MX2A/MX4A 15 Conductor Cable||2-9858-XXX|
|MX7B/MX7M 6 Conductor Cable||2-9873-XXX|
|MX7B/MX7M 15 Conductor Cable||2-9858-XXX|
The Televac® MX2A and MX4A are thermal conductivity gauges for rough vacuum measurement (1*10-3 Torr to 1000 Torr). The Televac® MX7B and MX7M are cold cathode gauges for high and ultra high vacuum measurement (1*10-11/1*10-8 Torr to 1*10-2 Torr).
Due to the design of cold cathodes, it is important that they are not turned on at pressures above 1*10-2 Torr. Turning the cold cathode on at higher pressures will lead to sputtering, oxidation, and contamination; these will cause inaccurate readings and damage to the sensor. Therefore, it is necessary to use a rough vacuum gauge, such as the MX2A or MX4A, to disable the cold cathode at pressures above 1*10-2 Torr.
The MX2A and MX4A both include relay set point, which is essentially a switch that can be set to a specific vacuum reading. In this case, the set point will be 1*10-2 Torr. The relay can be wired to the cold cathode’s voltage supply, creating an active gauge system capable of measuring from 1*10-11/1*10-8 Torr to 1000 Torr.
Configuring the MX2A/MX4A Set Point
Set point 2 has 2 settings:
1. SP2H (Set Point 2 High) – the vacuum reading where the set point deactivates
2. SP2L (Set Point 2 Low) – the vacuum reading where the set point activates
1. SP2H – 0.012 Torr (12 mTorr, 12 microns, 1.2*10-2 Torr)
2. SP2L – 0.010 Torr (10 mTorr, 10 microns, 1.0*10-2 Torr)
Note that these are just recommendations. Your system may require different settings.
To change the SP2H and SP2L settings, do the following:
1. Press the SEL button until the screen says “Setpoints”.
2. Use the up/down arrows until the screen says “SP2L”.
3. Press ENT. The top of the screen will now say “ADJ”.
4. Use the up/down arrows to adjust the value to the desired SP2L. In our recommendations above, this would be 0.010.
5. Press ENT again to save the change. The “ADJ” at the top of the screen will disappear.
6. Press the down arrow. The screen should now show SP2H. If it does not, press the arrows until it does.
7. Press ENT. “ADJ” will reappear on the top of the screen.
8. Use the up/down arrows to adjust the values to the desired SP2H. In our recommendations above, this would be 0.012.
9. Press ENT again to save the new setting. The “ADJ” at the top of the screen will disappear.
10. Press SEL until you reach the measurement screen or wait for the screen to timeout.
SP2H and SP2L can also be changed using the RS-485 W3 command. The following command will change SP2H and SP2L to our recommended values.
Note that X is the address of the unit (default 0) and <cr> is a carriage return (which is sent when the enter key is pressed):
Enabling Pin Control on the MX7B/MX7M
1. Press SEL until the screen says “System Settings”. If initially on the measurement screen, it should be pressed 2 times to reach this screen.
2. Press SEL until Vsense Control is shown on the screen. This should be the 4th setting.
3. Use the up and down arrows to set this to Pin Control.
This can also be done with the RS-485 W8 command. The following command will set the unit to pin control mode.
Note that X is the address of the unit (default 0) and <cr> is a carriage return (which is sent when the enter key is pressed).
Connecting the MX2A/MX4A to the MX7B/MX7M
The MX2A/MX4A’s relay will connect pins 11 and 3 when the pressure is above the setpoint, and will connect pins 11 and 4 when the pressure is below the setpoint. Therefore, this can be used to short pins 13 and 14. The following table and diagram show the connections that will allow the relay to control the MX7B/MX7M:
|Pin 11 (SP2 COM)||Pin 13|
|Pin 4 (SP2 NO)||Pin 14|
Note that it is necessary to supply power to units. Additionally, it may be necessary to connect to the analog or RS-485 connections depending on the application.