Using the below code to assign  sequence number for two different fields in the same class.

Method 1:

class easy_filedcb(osv.osv):
    _name="easy.filedcb"
    _columns={
        'file': fields.char('File', size=64),
        'dcb':fields.char('DCB', size=64),
        }

    def next_by_code(self, cr, uid, sequence_code, name, context=None):
        seq_obj = self.pool.get('ir.sequence')    
        seq_obj.check_access_rights(cr, uid, 'read')
        company_ids = self.pool.get('res.company').search(cr, uid, [], order='company_id', context=context) + [False]
        ids = seq_obj.search(cr, uid, ['&','&',('code','=', sequence_code),('name','=',name),('company_id','in',company_ids)])        
        return seq_obj._next(cr, uid, ids, context)
    
    def create(self, cr, uid, vals, context=None):
        if context is None:
            context = {}
        vals['file'] = self.next_by_code(cr, uid, 'easy.filedcb', 'file', context=context) or '/'  
        vals['dcb'] = self.next_by_code(cr, uid, 'easy.filedcb', 'dcb', context=context) or '/'  
        return super(easy_filedcb, self).create(cr, uid, vals, context=context)

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data noupdate="1">
       <record id="seq_easy_filedcb_type" model="ir.sequence.type">
            <field name="name">dcb</field>
            <field name="code">easy.filedcb</field>
        </record>    
        
        <record id="seq_dcbnumber" model="ir.sequence">
            <field name="name">dcb</field>
            <field name="code">easy.filedcb</field>
            <field name="prefix">D</field>
            <field name="padding">4</field>
        </record>
        
        <record id="seq_filenumber" model="ir.sequence">
            <field name="name">file</field>
            <field name="code">easy.filedcb</field>
            <field name="prefix">F</field>
            <field name="padding">4</field>
        </record>
    </data>
</openerp>

Method 2:

create second sequence with other object name (Any Master screen used in the custom module and sequence No does not used in that screen)  and call in the same class

EXample:-

 class easy_filedcb(osv.Model):
    _name="easy.filedcb"
    _columns={
        'file': fields.char('File', size=64,readonly=True),
        'dcb':fields.char('DCB', size=64,readonly=True),
        }
    
    def create(self, cr, uid, vals, context=None):
                   vals['dcb'] = self.pool.get('ir.sequence').get(cr, uid, 'easy.filedcb') or '/'
                   vals['file'] = self.pool.get('ir.sequence').get(cr, uid, 'other.mastername') or '/'
            return super(easy_filedcb, self).create(cr, uid, vals, context=context)
    

    _defaults = {
        'dcb': lambda obj, cr, uid, context: '/',
        'file': lambda obj, cr, uid, context: '/',  
                }
 
easy_filedcb()

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data noupdate="1">
 
        <record id="seq_easy_filedcb_type" model="ir.sequence.type">
            <field name="name">dcb</field>
            <field name="code">easy.filedcb</field>
        </record>
        <record id="seq_dcbnumber" model="ir.sequence">
            <field name="name">dcb</field>
            <field name="code">easy.filedcb</field>
            <field name="prefix">D</field>
            <field name="padding">4</field>
        </record>
            <record id="seq_easy_file_type" model="ir.sequence.type">
            <field name="name">file</field>
            <field name="code">other.mastername</field>
        </record>
        <record id="seq_filenumber" model="ir.sequence">
            <field name="name">file</field>
            <field name="code">other.mastername</field>
            <field name="prefix">F</field>
            <field name="padding">4</field>
        </record>
     </data>
</openerp>