4
PENBERTHY
MODEL MGT-362 LEVEL MEASUREMENT TRANSMITTER
INSTALLATION, OPERATION AND MAINTENANCE INSTRUCTIONS
8. The NULL potentiometer is properly set as
part of the factory calibration and should not
require any further adjustment.
CAUTION
Should the NULL require adjustment; care must
be taken to ensure that the potentiometer is not
over-ranged. The NULL potentiometer should be
set with the liquid in the vessel set to the 'zero'
point. A digital voltmeter should be connected
to test points TP1 (+) and TP2 (-). Slowly turn the
NULL potentiometer so that the reading on the
voltmeter approaches a reading of 0.0 volts. At
some point (usually within 0.1 Volts) the reading
on the meter will no longer respond to any
adjustment of the NULL potentiometer. At this
point, turn the NULL potentiometer back slightly,
so that the potentiometer is at the threshold of
meter response. The reading does not have to be
exactly 0.00 Volts.
Any additional adjustment of the NULL
potentiometer beyond the point described
above will decrease the available gain of the
current loop and hinder proper calibration.
9. Turn the OFFSET potentiometer (R14)
clockwise so that the millimeter reads 4mA
± 0.05mA. (See Figure 2)
10. Raise the liquid level to the highest possible
level. For bench calibration place the
float at the point on the sensing element
corresponding to 100% level.
11. Turn the SPAN potentiometer (R15)
clockwise so that the millimeter reads
20mA ± 0.05mA. (See Figure 2)
12. Lower the float or calibration magnet to
the 75%, 50% and 25% level. Verify that
the output goes to 16mA, 12mA, and 8mA
respectively.
13. Disconnect the power. Remove the
voltmeter and the millimeter from the unit.
Reconnect the positive (+) lead from the
power supply to TB2 (+). (See Figure 2)
FIGURE 2
MGT-362 PCB Details for Wiring and Calibration
5 TROUBLESHOOTING
5.1 Introduction
Your Penberthy Model MGT-362 transmitter
is designed to give you years of unattended
service. However, failure of electrical equipment
can occur. Sound maintenance practices
require periodic inspection of the instrument to
ensure it is in good working order.
WARNING
'Live' electrical circuits can ignite flammable
gases. Be sure that the unit is properly grounded
and that a suitable intrinsically safe barrier has
been installed between the power supply and this
unit. Failure to use a barrier can result in severe
personal injury or property damage.
5.2 Test procedure
Follow the procedure in Section 4.1. If this
doesn't solve the problem, go to Section 6.
