Ashcroft B7 series, Installation And Maintenance Manual

Page: 12 / 19

Page 12 of 19
After installation of the control replace cover to insure electrical safety and to protect internal parts from the
environment.
8.4.3 Differential pressure switch model D7 (low range)
A single setpoint adjustment nut (7⁄8˝) is located centrally at the bottom on the inside of the enclosure.
The direction of turning is indicated on a label affixed to the inside of the control enclosure. XG5 controls have a
setpoint indication scale adjacent to the adjustment nut. To adjust the control, align the top of the adjustment nut hex
with the indicator line on the scale. Do not force adjustment or attempt to exceed the maximum setting shown on the
scale or nameplate.
For accurate setpoint calibration or for controls without a scale mount the control on a calibration stand so that the
HIGH and LOW pressures expected under operating conditions may be obtained. Suitable reference standards are
necessary for each pressure.
Note – Due to the sensitivity of these controls it is imperative that the LOW pressure side volume be large
to prevent a setpoint shift between calibration and field installation. If this is not possible, an approximate
setpoint under operating conditions can be obtained by setting the operating point with the low side open to
atmosphere. A final setpoint adjustment can be made after installation.
Apply LOW pressure. Then apply HIGH pressure to the required setpoint and turn the adjustment nut until the switch
operates. When the setpoint has been achieved, raise and lower HIGH pressure to ensure that the differential
pressure between the HIGH and LOW pressures is correct.
After installation of the control, replace the cover to ensure electrical safety and to protect the internal parts from the
environment.
8.4.4 Temperature switch model T7
A single setpoint adjustment nut (7⁄8˝) is located centrally at the bottom on the inside of the enclosure.
The bulb of the control should be immersed in a bath at the desired setpoint temperature. Optimum performance will
be obtained if the bulb is fully immersed. Allow five minutes for initial stabilization.
As received, the temperature switch will normally be set to approximately 90% of the indicated range. After
stabilization, turn the adjustment nut until switch changes mode. Direction of turning is indicated on a label affixed to
the inside of the control enclosure. When setpoint has been achieved raise and lower temperature to insure that the
setpoint is correct.
After installation of the control replace cover to insure electrical safety and to protect internal parts from the
environment.
8.4.5 B750, D750 and T750 Variable Deadband Switches
Deadband is varied by rotating the wheel on the precision switch. When viewed from the front of the enclosure,
rotation to the left increases deadband – rotation to the right decreases deadband. Letters on the wheel may be used
as a reference. Deadbands obtainable will vary from 0.5% to 9% of pressure or temperature range depending on
range segment and type of diaphragm.
Adjustment of Setpoint – As received, the switch will normally be set to approximately 90% of range. Rotate the wheel
on the MICRO SWITCH all the way to the right; this will provide smallest deadband. Pressurize, or increase bath
temperature, to the required setpoint and turn the adjustment nut until the switch changes mode. Lower the pressure
to reset the switch. Rotate the wheel on the MICRO SWITCH until the desired deadband is obtained. The upper
setpoint will be changing upward with this adjustment. Lower the pressure to reset the switch. Then increase the
pressure to the desired setpoint and turn the adjusting nut until the switch changes mode. Lower the pressure and
check resetpoint and deadband.
8.5 Subsequent relocation of the switch (by the customer)
Recommendation: Do not remove the switch from one metering point and fit it in a different place, as
there is a risk of the measuring media being mixed, with unforeseeable chemical reactions.
9 Servicing
All ASHCROFT switches require little or no maintenance.
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Be sure that the case is closed at all times.