Hardware; Maintenance - Emerson Rosemount 248 Reference Manual

Section 4: Operation and Maintenance
March 2014
Output trim
Fast Key sequence
The D/A Trim command allows the transmitter's conversion of the input signal to a 4–20 mA
output to be altered (see
intervals to maintain measurement precision. To perform a digital-to-analog trim:
1.
2.
3.
4.
5.
6.
7.
Scaled output trim
Fast Key sequence
The Scaled D/A Trim command matches the 4 and 20 mA points to a user-selectable reference
scale other than 4 and 20 mA (2–10 volts, for example). To perform a scaled D/A trim, connect
an accurate reference meter to the transmitter and trim the output signal to scale as outlined in
the Output trim
4.3

Hardware

4.3.1

Maintenance

The Rosemount 248 has no moving parts and requires minimal scheduled maintenance.
Sensor checkout
To determine whether the sensor is at fault, replace it with another sensor or connect a test
sensor locally at the transmitter to test remote sensor wiring. Do not remove the thermowell
while in operation
consult the factory for a replacement special sensor and transmitter combination.
46
1, 2, 2, 2
Figure 4-1 on page
From the HOME screen, select 1 Device setup, 2 Diag/Service, 2 Calibration, 2 D/A trim.
Set the control loop to manual and select OK.
Connect an accurate reference meter to the transmitter at the CONNECT REFERENCE
METER prompt by shunting the power to the transmitter through the reference meter
at some point in the loop. Select OK after connecting the reference meter.
Select OK at the SETTING FLD DEV OUTPUT TO 4 MA prompt, then transmitter outputs
4.00 mA.
Record the actual value from the reference meter, and enter it at the ENTER METER
VALUE prompt. The communicator prompts the user to verify whether or not the
output value equals the value on the reference meter.
If the reference meter value equals the transmitter output value, select 1 Yes and go to
Step 6. If the reference meter value is not equal to the transmitter output value, select 2
No and go to Step 4.
Select OK at the SETTING FLD DEV OUTPUT TO 20 MA prompt and repeat steps
until the reference meter value equals the transmitter output value.
Return the control loop to automatic control and select OK.
1, 2, 2, 3
procedure.
Select any standard, off-the-shelf sensor for use with a Rosemount 248, or
.
45). Adjust the analog output signal at regular
Operation and Maintenance
Reference Manual
00809-0100-4825, Rev CB
4 and 5