DC Current monitoring at metal body paint shops


Metal goods or commodities are paint coated in order to avoid rusting or degradation of surface quality, this also increases the aesthetics of commodities. Various methods are used for this application. The life as well as durability of paint depends on the method of paint deposition. New techniques are always implemented to improve the surface coating of metal jobs. Electrodeposition of paint is one such innovative method of paint deposition. It is used for the coating of merchandise ranging in size from steel building trusses and automobile bodies, metal furniture, appliances and toys, to objects as small as nuts and bolts. The acceptance of this coating technology is still accelerating as more and more industries realize the inherent advantages of the process.

Problem Statement

In the process of electrodeposition of paint molecules, various gases are released which affect the DC current flowing in the process at the given applied voltage. It is necessary to monitor this current to monitor the deposition intensity. A PLC based system can be used as a control system to regulate the flow of current. Variation in current flowing through the system may lead to uneven thickness of paint film on the surface of the metal body.

Present Scenario

There are no monitoring systems installed in this application as present due to unavailability of a proper and accurate measuring instrument.


  • It is essential to use an instrument capable of measuring DC current as an input from the electrodeposition process
  • To cater such needs a relevant product – Rishabh’s highly accurate DC current monitoring shunts are used
  • A shunt is connected in series with the electrodeposition unit, the output of shunt is in mV and is fed to signal isolator TV808
  • The output of TV808 is a signal compatible for PLCs as input for further controlling


The method of electrodeposition is used to coat fabricated metal jobs of automobile parts, switchgears, metal furniture, etc. The deposition process involves a DC source of supply and cathodic process of coating is implemented. As the current passes through the apparatus the polymer molecules break and decompose on the metal part. The film deposition prior to the baking process is of utmost importance as the intensity of current decides the film thickness and evenness. The current flowing through apparatus is generally constant but due to high resistance gas development, the current changes. This calls for a need of a DC current measurement instrument as well as a device which can control the flow of current to have a uniform layer of paint coat. 

Therefore a DC Shunt is connected in series with the circuit and its mV drop is fed to a PLC via a signal isolator, PLCs are used to control the applied voltage such that current remains effectively present to provide uniform painting.  Logical ladder diagram is written in a PLC system to execute this procedure.


  • Continuous DC current monitoring with precise and accurate Rishabh Shunts
  • Signal isolation and a wide combination of PLC compatible DC signals as output from TV808 – Signal Isolator 

Schematic Representation