Precision Measurement Engineering, Inc.

Discussing SCAMP Maintenance

REPLACING A SENSOR

1. Drain and remove the sensor cover.
   
   
2. Open the SCAMP.  See Opening the SCAMP section for more detailed information.   This is a delicate operation since the sensors are exposed at this time.   Insure no residual water droplets run down into the electronics region.
   
   
3. Clamp the SCAMP electronics horizontally in two vises by clamping the chassis, not the electronics covers. The sensor being replaced should be up. The following pictures show the Fast Temperature sensor (5316) with its associated resistor.  Use two vises.   If one vise is used, and the SCAMP clamped in the middle, it will unexpectedly slip and rotate the sensors into the table top. 
   
   
4. Remove the electronics cover. See Removing and Replacing the Electronics Covers section for more detailed information.
   
   
   
   
   
   
5. Cut the wires from the sensor being replaced so that 1/4" of colored insulator remain attached to the post. This will indicate the proper wiring of the new sensor. Click on the picture for a more detailed image.
   
   
   
   
   
   
6. Use the pliers to gently unscrew (counter clockwise seen from the sensor side) the sensor sealing nut. Slide this nut up the sensor shaft.
   
   
   
   
   
   
7. Loosen the set screw in the chassis end plate that mechanically retains the sensor.
   
   
   
   
   
   
8. Rotate the sensor so that it is not near the other sensors.
   
   
   
   
   
   
9. Gently pull the sensor out of the endcap being careful that the wires don't crash the other sensors.. Place a protective cover on it.
   
   
   
   
   
10. Installing the new sensor. Inspect the wires-end of the shaft to make sure that there are no burrs, glue, other foreign materials, or scratches in the area where the seal is made. Remove the plastic thermistor cover.  This is a very delicate operation!!  Place the retaining nut on the shaft. The image below shows a Fast Temperature sensor.
    
    
    
    
    
    
11. Gently slide the sensor into the endcap.
    
    
    
    
    
    
12. Position the sensor properly. You may be required to bend the sensor shaft somewhat if close alignment is desired. Tighten the set screw when this is accomplished.
    
    
    
    
    
    
13. Tighten the sealing nut firmly with pliers. CAREFUL! THE RETAINING NUT MAY SHIFT THE SENSOR POSITION SLIGHTLY OR TWIST THE SENSOR IF THE RETAINING SCREW IS NOT TIGHT CAUSING THE SENSOR TO CRASH INTO THE OTHERS.
    
    
    
    
    
    
14. Cut the sensor wires to the appropriate length (leave a long loop) and strip the last 1".  New sensors should already have the wires stripped at the correct length.  If a wire must be stripped and the proper 30 gauge stripping tool is unavailable the insulation can be removed by melting through it with a soldering iron while pulling on the wire.  One at a time unwind the old sensor wire and replace it with the same color new sensor wire. Remember when replacing the Fast Temperature sensor that there is a resistor to replace as well.  Use the wire wrapping tool supplied by PME to wire wrap the new wires. DO NOT SOLDER!
    
    
    
    
    
    
15. Replace the electronics cover. See Removing and Replacing the Electronics Covers section for more detailed information.
    
    
    
    
    
    
16. Examine the o-rings as described in the Inspecting the O-rings section.
    
    
    
17. Insert the SCAMP electronics back into the tube until the o-rings engage.
    
    
    
    
    
    
18.  Replace the closure ring and tighten it, pulling the SCAMP electronics completely into the tube. Only tighten this ring until the electronics are completely in the tube. Loosen the ring slightly so that it will be easy to unscrew at a later date.
    
    
     
    
    
    
19. Replace the sensor cover. Pressurize the interior as described in the leak test, then partially fill the sensor cover with water.   Carefully check for bubbles exiting between the sealing nut and sensor shaft.. If bubbles appear, then drain and remove the cover.  Re-tighten the sealing nut. This nut is only plastic so don't tighten it too much.  Repeat the leak test.
    
    
    
    
    
    
20. If bubbles persist, then follow the above steps to remove the sensor. Inspect the sensor shaft. Remove the teflon ferrule within the endcap hole and replace it.  Repeat the procedure.
    
    
21. Now that the sensor is physically installed on the SCAMP, its calibration must be installed into the software. This is done by using the SCAMP Control Dialog’s Channel Tab to place the correct values into the C0…C3 and NOFF, NOFFPOLAR, and NGAIN boxes. Calibrated sensors supplied by PME will have documentation that give these values. User supplied sensors must be calibrated and the results placed here.