Knowledge Base:  
Tech Note 110: Troubleshooting CMCP420VT(T)
Last Updated: 05/10/2017

Troubleshooting CMCP420VT(T)Bench testing a CMCP420VT(T) is quite easy and can be accomplished using a 24 VDC power supply and a DVM (Digital Volt Meter) in mA (Amp) mode. Be sure that the fuse in the mA input of your DVM is good. Most quality DVM’s have a 1 and 10 Amp selection. Select the lowest as you will only be measuring to about 30 mA or 0.030 Amp. Be sure the power supply is wired plus to plus and minus to minus to the CMCP420VT. The DVM can be inserted in series in either leg.

***** Important *****
The CMCP420VT requires a minimum voltage dependant on resistance in the loop. If units locks at >21 mA voltage needs to be increased by using an external +24 VDC power supply.

In the case of the CMCP420VT-T with Temperature the loop mA is checked the same way, just move the wires to the temperature side of the terminal. Heat the unit gently with a heat gun or your hand and mA output will increase. Allow time for unit to heat soak and do not overheat.

The CMCP420VT will begin operation as soon as 24 VDC power is supplied. Start up time is short but give the unit about 30 seconds for the integrator to settle. At rest on a table or desk top the unit should read about 4.0 mA (0.004 Amp) depending on floor and table vibration. Tap the unit gently against the table at a rate of a couple times per second. Increasing the force of the taps will cause the unit to read over 20 mA (0.020 Amps).

Loop Test Setup


Problem

Solution

No Output

Verify Wiring
Verify Supply Voltage at V+ Terminal (18 to 36 VDC)
Verify Loop with DVM in Series (mA Mode)
Verify PLC/DCS Scaling (4 mA = 0, 20 mA =1.00)
Verify External Power Supply Common is Established (If Used)
Replace with Spare

Output Locked at >21 mA

Inadequate Supply Voltage
Verify Supply Voltage at V+ Terminal (18 to 36 VDC)
Increase Supply Voltage as Required

Low Vibration Reading

Verify with Portable Meter
Verify PLC/DCS Scaling (4 mA = 0, mA =1.00)
Verify Sensor is Correctly Positioned on Bearing

High Vibration Reading

Verify with Portable Meter
Verify PLC/DCS Scaling (4 mA = 0,20 mA =1.00)
Repair Machine or Adjust Process

Erratic Measurement

Verify with Portable Meter
Verify Unit is Mounted Securely
Verify Wiring and Intermediate Terminals



Was this article helpful?

Comments:
 

Related Articles
 > Tech Note 101: Wiring CMCP1100 (ICP) Accelerometers
 > Tech Note 102: Powering – 24 VDC Eddy Probes
 > Tech Note 103: Accelerometer Powering with CCD Diode
 > Tech Note 104: Wiring Relays with Common Alarms
 > Tech Note 105: Reversing Normal Thrust Direction CMCP545(A)
 > Tech Note 106: Recalibrating CMCP505 Digital Displays >01/01/07
 > Tech Note 108: Installation of Accelerometer Extension Cables
 > Tech Note 107: Recalibrating CMCP505 Digital Displays <01/01/07
 > Tech Note 109: Troubleshooting 500 Series Transmitters
 > Tech Note 111: CMCP510 Display Calibration
 > Tech Note 112: Vibration Severity Level ISO 10816-1
 > Tech Note 113: CMCP420VT(T) Compliance
 > Tech Note 114: Double Integration of Vibration Signals
 > Tech Note 115: Shunt Resistors
 > Tech Note 116: Electro-Mechanical Velocity Sensors
 > Tech Note 117: ISO Standard 10816-3
 > Tech Note 118: What We Need to Know!
 > Tech Note 119: CMCP420VT Buffered Output
 > Tech Note 120: CMCP575 Tachometer Precision Calibration
 > Tech Note 121: Magnetic Bases for Accelerometers
 > Tech Note 122: Double Integration
 > Tech Note 123: Calculating Transmitter Ranges
 > Tech Note 124: Cable Grounding (Isolated and Non-Isolated Shields)